Lubricants for refrigeration systems
View Patent ↗A polyol ester suitable for use as a lubricant or a lubricant base stock has a kinematic viscosity at 40° C. greater than or equal to 200 cSt and a viscosity index of greater than or equal to 100. The ester comprises the reaction product of (a) a polyhydric alcohol component comprising at least 50 mole % of penterythritol, and (b) a carboxylic acid component comprising: (i) at least one linear or branched monocarboxylic acid having 2 to 7 carbon atoms; (ii) at least one branched monocarboxylic acid having 8 to 15 carbon atoms; and (iii) at least one polycarboxylic acid having 2 to 8 carbon atoms; wherein the ratio of the number of acid groups derived from the monocarboxylic acid(s) (i) to the number of acid groups derived from the monocarboxylic acid(s) (ii) is between about 0.9 and about 1.1 and the number of acid groups derived from the polycarboxylic acid(s) (iii) is between about 15% and about 25% of the total number of acid groups derived from the carboxylic acids (i), (ii) and (iii).
1. A polyol ester suitable for use as a lubricant or a lubricant base stock, the ester having a kinematic viscosity at 40° C. greater than or equal to 200 cSt and a viscosity index of greater than or equal to 100 and the ester comprising a reaction product of (a) a polyhydric alcohol component comprising at least 90 mole % of penterythritol, and (b) a carboxylic acid component comprising:
(i) at least one linear or branched monocarboxylic acid having 5 to 7 carbon atoms;
(ii) at least one branched monocarboxylic acid having 8 to 12 carbon atoms; and
(iii) at least one polycarboxylic acid having 2 to 8 carbon atoms;
wherein the ratio of the number of acid groups derived from the monocarboxylic acid(s) (i) to the number of acid groups derived from the monocarboxylic acid(s) (ii) is between about 0.9 and about 1.1 and the number of acid groups derived from the polycarboxylic acid(s) (iii) is between about 15% and about 25% of the total number of acid groups derived from the carboxylic acids (i), (ii) and (iii).
2. The ester of claim 1 , wherein the polyhydric alcohol component comprises at least 95 mole % of penterythritol.
3. The ester of claim 1 , wherein said at least one linear or branched monocarboxylic acid (i) is selected from n-pentanoic acid, i-pentanoic acid, n-hexanoic acid, i-hexanoic acid, n-heptanoic acid and i-heptanoic acid.
4. The ester of claim 1 , wherein said at least one branched monocarboxylic acid (ii) comprises i-nonanoic acid (3,5,5-trimethylhexanoic acid).
5. The ester of claim 1 , wherein said at least one polycarboxylic acid (iii) has 4 to 7 carbon atoms.
6. The ester of claim 1 , wherein said at least polycarboxylic acid (iii) comprises adipic acid.
7. The ester of claim 1 , wherein the ratio of the number of acid groups derived from the monocarboxylic acid(s) (i) to the number of acid groups derived from the monocarboxylic acid(s) (ii) is between about 0.9 and about 0.95.
8. The ester of claim 1 , wherein the ratio of the number of acid groups derived from the monocarboxylic acid(s) (i) to the number of acid groups derived from the monocarboxylic acid(s) (ii) is about 0.93.
9. The ester of claim 1 , wherein the number of acid groups derived from the polycarboxylic acid(s) (iii) is between about 19% and about 21% of the total number of acid groups derived from the carboxylic acids (i), (ii) and (iii).
10. A lubricant blend comprising a mixture of the polyol ester of claim 1 and a further polyol ester having a different kinematic viscosity than said first mentioned polyol ester.
11. A working fluid comprising a halogenated hydrocarbon refrigerant and the polyol ester of claim 1 .
12. The working fluid of claim 11 wherein the refrigerant is a hydrofluorocarbon, a fluorocarbon or a mixture thereof.