Low pour point trimethylolpropane esters

Abstract

The present invention relates to polyol esters that are particularly suitable for use as insulating oils in electrical equipment where an effective cooling action is required, such as electrical transformers. In particular the invention relates to esters of trimethylolpropane with monocarboxylic acids of nine and/or ten carbon atoms, wherein the monocarboxylic acids of nine and/or ten carbon atoms comprise 5-15 mol % of branched acids and 85-95 mol % of linear acids with respect to the total moles of the monocarboxylic acids.

Claims

1. An ester of trimethylolpropane with monocarboxylic acids of nine and/or ten carbon atoms, said monocarboxylic acids of nine and/or ten carbon atoms comprising 5-15 mol % of a branched acid and correspondingly 85-95 mol % of pelargonic acid with respect to the total moles of the said monocarboxylic acids, said ester having a kinematic viscosity at 40° C. of less than 35 mm.sup.2/s and having a pour point according to standard ISO 3016 of below −40° C.

2. The ester according to claim 1 having a kinematic viscosity at 40° C. of less than 30 mm.sup.2/s.

3. The ester according to claim 1 having a pour point according to standard ISO 3016 of below −45° C.

4. The ester according to claim 1 having a flash point according to standard ISO 2719 (Pensky-Martens, closed cup procedure) of above 200° C.

5. The ester according to claim 1 wherein said branched acid is selected from 3,5,5-trimethylhexanoic acid, 7-methyloctanoic acid, 2,2-dimethylheptanoic acid, 3,3-dimethylheptanoic acid, 8-methylnonanoic acid, 2,2-dimethyloctanoic acid and mixtures thereof.

6. The ester according to claim 1 having an hydroxyl number equal to or less than 2 mg KOH/g.

7. A process for the preparation of an ester according to claim 1 comprising the esterification of trimethylolpropane with monocarboxylic acids of nine and/or ten carbon atoms comprising 5-15 mol % of a branched chain and 85-95 mol % of pelargonic acid.

8. The process according to claim 7 wherein said esterification is carried out in the absence of catalyst.

9. A process for the preparation of an ester according to claim 1 comprising the transesterification of trimethylolpropane with alkyl esters of monocarboxylic acids having nine and/or ten carbon atoms comprising 5-15 mol % of a branched chain and 85-95 mol % of pelargonic acid.

10. An insulating oil comprising an ester according to claim 1 and an additive and/or another insulating oil.

11. An insulating oil comprising an ester of trimethylolpropane according to claim 1.

12. The insulating oil according to claim 11 further comprising one or more additives selected from the group consisting of antioxidants, antistatic agents, hydrolysis inhibitors, antimicrobial agents, antifoaming agents, metal passivators, extreme pressure additives, pour point depressants, and anti-wear additives.

13. The ester according to claim 2 having a pour point according to standard ISO 3016 of below −45° C.

14. The ester according to claim 2 having a flash point according to standard ISO 2719 (Pensky-Martens, closed cup procedure) of above 200° C.

15. The ester according to claim 3 having a flash point according to standard ISO 2719 (Pensky-Martens, closed cup procedure) of above 200° C.

16. The ester according to claim 2 wherein said branched acid is selected from 3,5,5-trimethylhexanoic acid, 7-methyloctanoic acid, 2,2-dimethylheptanoic acid, 3,3-dimethylheptanoic acid, 8-methylnonanoic acid, 2,2-dimethyloctanoic acid and mixtures thereof.

17. The ester according to claim 3 wherein said branched acid is selected from 3,5,5-trimethylhexanoic acid, 7-methyloctanoic acid, 2,2-dimethylheptanoic acid, 3,3-dimethylheptanoic acid, 8-methylnonanoic acid, 2,2-dimethyloctanoic acid and mixtures thereof.

18. The ester according to claim 1, wherein said branched acid is selected from 3,5,5-trimethylhexanoic acid.

19. The ester according to claim 18, which comprises 8-12 mol % of the branched acid and correspondingly 88-92 mol % of pelargonic acid with respect to the total moles of the said monocarboxylic acids.

20. The ester according to claim 18, which comprises 9-11 mol % of the branched acid and correspondingly 89-91 mol % of pelargonic acid with respect to the total moles of the said monocarboxylic acids.

21. The ester according to claim 1, which comprises 8-12 mol % of the branched acid and correspondingly 88-92 mol % of pelargonic acid with respect to the total moles of the said monocarboxylic acids.

22. The ester according to claim 1, which comprises 9-11 mol % of the branched acid and correspondingly 89-91 mol % of pelargonic acid with respect to the total moles of the said monocarboxylic acids.

23. The ester according to claim 1 having a kinematic viscosity at 40° C. of less than 25 mm.sup.2/s and having a pour point according to standard ISO 3016 of below −51° C.

24. A method for preparing an insulating oil, from a trimethylolpropane ester with monocarboxylic acids having nine and/or ten carbon atoms, said monocarboxylic acids of nine and/or ten carbon atoms comprising 5-15 mol % of a branched acid and 85-95 mol % of correspondingly pelargonic acid with respect to the total moles of the said monocarboxylic acids, said ester having a kinematic viscosity at 40° C. of less than 35 mm.sup.2/s and having a pour point according to standard ISO 3016 of below −40° C.; comprising at least one purification operation selected from the group consisting of dehydration, decolouring, deacidification and filtration.

25. An electrical apparatus comprising at least one insulating oil according to claim 11.

Description

EXAMPLES

Example 1

(1) A trimethylolpropane ester with carboxylic acids having nine carbon atoms according to the invention was prepared by placing:

(2) 26.3 g of trimethylolpropane,

(3) 108 g of nonanoic acid (purity >99%)

(4) 12 g of 3,5,5-trimethylhexanoic acid (linear:branched acid molar ratio=90:10) in a glass reactor equipped with an electric heating jacket, a condenser and a mechanical stirrer.

(5) During the synthesis the temperature of the reaction medium was increased to 240° C.

(6) During the final reaction stage the pressure was reduced to 200 mbar to encourage the removal of water. On completion of the reaction the product was purified, the excess acids being evaporated by means of a further reduction in pressure to 10 mbar and the residual acidity neutralised by treatment with calcium hydroxide.

(7) The product underwent a further purification treatment using a Fuller's earth (sepiolite) and A4 molecular sieves in order to reduce the acidity and water content.

(8) Table 1 shows the properties of the product obtained, measured according to the methods indicated, before and after the addition of a quantity of 0.3% by weight of a primary phenol antioxidant (Irganox® 1010, marketed by BASF SE):

(9) TABLE-US-00001 TABLE 1 TMP-C9 TMP-C9 C9-isoC9 = 90:10 C9-isoC9 = 90:10 ANALYSIS METHOD without additive with additive Appearance VISUAL Clear liquid free Clear liquid free of suspended of suspended solids solids Viscosity at 40° C. ISO 3104 21.39 21.39 (mm.sup.2/s) Density at 15° C. ISO3675 0.944 0.944 (g/ml) Pour point (° C.) ISO 3016 <−54 <−54 Water content (ppm) IEC 60814 46.7 36.7 Discharge voltage IEC 60156 86 77 (2.5 mm gap) (kV) Dissipation factor IEC 60247 0.03084 0.02854 (tan δ 90° C.) Resistivity IEC 60247 6.3 6.2 (GΩ × m at 90° C.) Total acidity IEC 62021-1 0.0101 0.0039 (mgKOH/g) Flash point ISO 2719 220 — (closed cup) (° C.)

(10) On the basis of the properties measured the product obtained is therefore suitable for use as transformer oil. In particular, in comparison with a trimethylolpropane ester with a nonanoic acid (which has a viscosity of 20.5 mm.sup.2/s and a pour point of −42° C. measured under the same conditions) the ester according to the invention has similar viscosity values and a significantly lower pour point. Together with these viscosity and pour point values the ester according to the invention has a flash point which is in any event over 200° C., in line with that of ester-based insulating oils in common use.

Examples 2-3

(11) Two trimethylolpropane esters with carboxylic acids having nine carbon atoms according to the invention were prepared in the same manner as in Example 1 but varying the linear: branched acid molar ratio from 95:5 (Example 2) to 85:15 (Example 3).

(12) Thus respectively 114 g of nonanoic acid and 6 g of 3,5,5-trimethylhexanoic acid in Example 2 and 102 g of nonanoic acid and 18 g of 3,5,5-trimethylhexanoic acid in Example 3 were esterified with 26.3 g of trimethylolpropane.

(13) The kinematic viscosity at 40° C., pour point and flash point properties of the obtained products (without additives), measured according to the same methods indicated in Table 1, are comparable to those of Example 1, as shown in Table 2.

Example 4

(14) A trimethylolpropane ester with carboxylic acids having nine and ten carbon atoms according to the invention was prepared in the same operating manner as in Example 1 by esterifying:

(15) 26.3 g of trimethylolpropane,

(16) 108,8 g of nonanoic acid (purity >99%)

(17) 13,7 g of iso-decanoic acid (linear:branched acid molar ratio=90:10).

(18) After purification treatment using a Fuller's earth (sepiolite) and A4 molecular sieves, the viscosity at 40° C. (according to ISO 3104), pour point (according to ISO 3016) and Flash point (closed cup; according to ISO 2719) of the resulting ester were measured. Results are reported in Table 2.

Example 5—Comparative

(19) A trimethylolpropane ester with carboxylic acids having nine carbon atoms and a linear: branched acid molar ratio of 10:90 was prepared in the same operating manner of Example 1, by esterifying

(20) 26.3 g of trimethylolpropane,

(21) 12 g of nonanoic acid (purity >99%)

(22) 108 g of 3,5,5-trimethylhexanoic acid.

(23) As can be seen from Table 2, the resulting trimethylolpropane esters of Example 5-comparative showed a viscosity at 40° C. considerably higher than 35 mm.sup.2/s and a pour point temperature above −45° C., which render them unsuitable for use as transformer oil.

(24) TABLE-US-00002 TABLE 2 Example 5- Example 2 Example 3 Example 4 comparative ANALYSIS (C9:iso-C9 = 95:5) (C9:isoC9 = 85:15) (C9-isoC10 = 90:10) (C9:isoC9 = 10:90) Appearance Clear liquid free Clear liquid free Clear liquid free of Clear liquid free of suspended of suspended suspended solids of suspended solids solids solids Viscosity at 21.49 22.29 21.07 44.31 40° C. (mm.sup.2/s) Pour point −48 <−55 −47 −42 (° C.) Flash point 222 225 227 229 (closed cup) (° C.)