Refrigeration compressor lubricant

1. A working fluid for a refrigeration system comprising a compressor, the working fluid comprising:

(i) an ester based lubricant comprising:

an ester mixture comprising (a) from 30 to 70% by weight of one or more first ester compounds, (b) from 30 to 70% by weight of one or more second ester compounds, wherein the (a) one or more first ester compounds and the (b) one or more second ester compounds of the ester mixture together form at least 50% by weight of the (i) ester based lubricant, and

(a) the one or more first ester compounds have a structure

wherein each of x, y, and z is independently an integer 2 to 8; and R 7 , R 8 , and R 9 are each independently selected from the group consisting of: straight-chain and branched alkyl, alkenyl, cycloalkyl, aryl, alkylaryl, arylalkyl, alkylcycloalkyl, cycloalkylalkyl, arylcycloalkyl, cycloalkylaryl, alkylcycloalkylaryl, alkylarylcycloalkyl, arylcycloalkylalkyl, arylalkylcycloalkyl, cycloalkylalkylaryl, and cycloalkylarylalkyl groups having 1 to 17 carbon atoms that may be substituted or unsubstituted;

(b) the one or more second ester compounds have a structure

wherein m is is an integer 1 to 10; and R 10 and R 13 are each independently selected from the group consisting of: straight-chain and branched alkyl, alkenyl, cycloalkyl, aryl, alkylaryl, arylalkyl, alkylcycloalkyl, cycloalkylalkyl, arylcycloalkyl, cycloalkylaryl, alkylcycloalkylaryl, alkylarylcycloalkyl, arylcycloalkylalkyl, arylalkylcycloalkyl, cycloalkylalkylaryl, and cycloalkylarylalkyl groups having 1 to 17 carbon atoms that may be substituted or unsubstituted;

(c) an additive selected from the group consisting of: diaryl sulfides, arylalkyl sulfides, dialkyl sulfides, diaryl disulfides, arylalkyl disulfides, dialkyl disulfides, diaryl polysulfides, arylalkyl polysulfides, dialkyl polysulfides, dithiocarbamates, derivatives of 2-mercaptobenzothiazole, derivatives of 2,5-dimercapto-1,3,4-thiadiazole, and combinations thereof; and

(ii) a refrigerant selected from the group consisting of: C 3 -C 8 hydrocarbons, trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), saturated hydrofluorocarbons, difluoromethane (HFC-32), 1,1,2,2-tetrafluoroethane (HFC-134), difluoroethane (HFC-152a), fluoroethane (HFC-161), R410A (a near-azeotropic mixture of difluoromethane (HFC-32) and pentafluoroethane (HFC-125)), 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), 1,1,1,2,3,3-hexafluoropropane (HFC-236ea), 1,1,1,3,3,3-hexafluoropropane (HFC-236fa), 1,1,1,3,3-pentafluoropropane (HFC-245fa), 1,1,1,3,3-pentafluorobutane (HFC-365mfc), hydrofluoroolefins, dimethyl ether, carbon dioxide, bis(trifluoromethyl)sulfide, and trifluoroiodomethane and combinations thereof, wherein the working fluid has a minimum miscibility temperature of about −55° C. or lower.

2. The working fluid of claim 1 , wherein the (a) one or more first ester compounds and the (b) one or more second ester compounds of the (i) ester based lubricant is an ester formed from a carboxylic acid selected from the group consisting of: n-pentanoic acid, 2-methylbutanoic acid, n-hexanoic acid, n-heptanoic acid, 3,3,5-trimethylhexanoic acid, 2-ethylhexanoic acid, n-octanoic acid, n-nonanoic acid, and isononanoic acid, and combinations thereof.

3. The working fluid of claim 1 , wherein the ester mixture comprises

(a) from about 40 to about 60% by weight of the one or more first ester compounds

wherein R 7 , R 8 , and R 9 are each independently selected from the group consisting of: straight-chain and branched alkyl and straight-chain and branched alkenyl groups having 3 to 8 carbon atoms that may be substituted or unsubstituted; and

(b) from about 40 to about 60% by weight of the one or more second ester compounds

wherein m is an integer 2 to about 8; and R 10 and R 13 are each independently selected from the group consisting of: straight-chain and branched alkyl and straight-chain and branched alkenyl groups having 3 to 8 carbon atoms that may be substituted or unsubstituted.

4. The working fluid of claim 1 , wherein the refrigerant is a C 3 -C 8 hydrocarbon selected from the group consisting of: propane, n-butane, isobutene, 2-methylbutane, n-pentane and combinations thereof.

5. The working fluid of claim 1 , wherein the refrigerant is a hydrofluoroolefin that is a C 2 to C 8 fluoroalkene selected from the group consisting of: 3,3,3,-trifluoropropene (HFO-1234zf), 2,3,3,3,-tetrafluoropropene (HFO-1234yf), 1,2,3,3,-tetrafluoropropene (HFO-1234ze), cis- and trans-1,3,3,3, -tetrafluoropropene (HFO-1234ye), 1,1,3,3,3,-pentafluoropropene (HFO-1225zc), 1,2,3,3,3,-pentafluoropropene (HFO-1225yez), CF 3 CCl═CH 2 (HFO-1233xf), CF 3 CH=CHCl (HFO-1233zd) and combinations thereof.

6. The working fluid of claim 1 , wherein the refrigerant is selected from the group consisting of: difluoromethane (HFC-32), R410A (a near-azeotropic mixture of difluoromethane (HFC-32) and pentafluoroethane (HFC-125)), and combinations thereof, wherein the working fluid has a miscibility range for HFC-32 and R410A of about −60° C. to about 50°.

7. The working fluid of claim 1 , wherein the ester based lubricant further includes an additional additive or additives selected from the group consisting of: antioxidants, anti-wear agents, extreme-pressure agents, oiliness agents, antifoaming agents, metal inactivating agents, viscosity index improvers, pour point depressants, detergent dispersants, stabilizers, metal passivators, corrosion inhibitors, flammability suppressants, acid scavengers, and combinations thereof.

8. The working fluid of claim 1 , where the additive comprises 2,5-dimercapto-1,3,4-thiadiazole.

9. A working fluid for a refrigeration system comprising a compressor, the working fluid comprising:

(i) an ester based lubricant comprising an ester mixture comprising (a) from 30 to 70% by weight of one or more first ester compounds, (b) from 30 to 70% by weight of one or more second ester compounds, wherein the (a) one or more first ester compounds and the (b) one or more second ester compounds of the ester mixture together form at least 50% by weight of the (i) ester based lubricant, and

(a) the one or more first ester compounds have a structure

 wherein x, y, and z are each independently an integer 2 to 4; and R 7 , R 8 , and R 9 are each independently selected from the group consisting of: straight-chain and branched-chain alkyl, straight-chain and branched-chain alkenyl groups having 3 to 8 carbon atoms that may be substituted or unsubstituted;

(b) the one or more second ester compounds have a structure

 wherein m is an integer 3 to 5; and R 10 and R 13 are each independently selected from the group consisting of: straight-chain and branched-chain alkyl, and straight-chain and branched-chain alkenyl groups having 3 to 8 carbon atoms that may be substituted or unsubstituted; and

(c) an additive selected from the group consisting of: diaryl sulfides, arylalkyl sulfides, dialkyl sulfides, diaryl disulfides, arylalkyl disulfides, dialkyl disulfides, diaryl polysulfides, arylalkyl polysulfides, dialkyl polysulfides, dithiocarbamates, derivatives of 2-mercaptobenzothiazole, derivatives of 2,5-dimercapto-1,3,4-thiadiazole, and combinations thereof, wherein the (i) ester based lubricant is present at less than or equal to about 50% by weight of the working fluid; and

(ii) a refrigerant selected from the group consisting of: difluoromethane (HFC-32), R410A (a near-azeotropic mixture of difluoromethane (HFC-32) and pentafluoroethane (HFC-125)), and combinations thereof, wherein the refrigerant is present at greater than or equal to about 50% by weight of the working fluid, wherein the working fluid has a minimum miscibility temperature of about −60° C. or lower.

10. The working fluid of claim 9 , wherein the additive is present in the ester based lubricant at about 0.1 to about 5% by weight.

11. The working fluid of claim 9 , wherein the additive is selected from the group consisting of: 2,5-bis(n-octyldithio)-1,3,4-thiadiazole, dioctyl disulfide, and combinations thereof.

12. The working fluid of claim 9 , wherein the ester based lubricant is present at greater than or equal to about 1% to less than or equal to about 30% of the working fluid and the refrigerant is present at greater than or equal to about 70% to less than or equal to about 99% by weight.

13. A working fluid for a refrigeration system comprising a compressor, the working fluid consisting essentially of:

(i) an ester based lubricant comprising an ester mixture comprising (a) from 1 to 99% by weight of a first ester compound comprising a glycerol ethoxylate ester formed by esterification with 3,3,5-trimethylhexanoic acid, (b) from 1 to 99% by weight of one or more second ester compounds comprising a triethylene glycol ester formed by esterification with 3,3,5-trimethylhexanoic acid, a tetraethylene glycol ester formed by esterification with 3,3,5-trimethylhexanoic acid, or a combination of a triethylene glycol ester formed by esterification with 3,3,5-trimethylhexanoic acid and a tetraethylene glycol ester formed by esterification with 3,3,5-trimethylhexanoic acid, wherein the (a) first ester compound and the (b) one or more second ester compounds of the ester mixture together form at least 50% by weight of the (i) ester based lubricant and where a major portion of the (i) ester based lubricant is the (a) first ester compound; and

(c) less than or equal to about 5% of an additive selected from the group consisting of: diaryl sulfides, arylalkyl sulfides, dialkyl sulfides, diaryl disulfides, arylalkyl disulfides, dialkyl disulfides, diaryl polysulfides, arylalkyl polysulfides, dialkyl polysulfides, dithiocarbamates, derivatives of 2-mercaptobenzothiazole, derivatives of 2,5-dimercapto-1,3,4-thiadiazole, and combinations thereof; and

(d) less than or equal to about 5% of an additional additive or additives selected from the group consisting of: antioxidants, anti-wear agents, extreme-pressure agents, oiliness agents, antifoaming agents, metal inactivating agents, viscosity index improvers, pour point depressants, detergent dispersants, stabilizers, metal passivators, corrosion inhibitors, flammability suppressants, acid scavengers, and combinations thereof, wherein the (i) ester based lubricant is present at less than or equal to about 50% by weight of the working fluid; and

(ii) a refrigerant present at greater than or equal to about 50% by weight of the working fluid.

14. The working fluid of claim 13 , wherein the additive is selected from the group consisting of: 2,5-bis(n-octyldithio)-1,3,4-thiadiazole, dioctyl disulfide, and combinations thereof.

15. The working fluid of claim 13 having a minimum miscibility temperature of about −55° C. or lower.

16. The working fluid of claim 13 , wherein the refrigerant is selected from the group consisting of: difluoromethane (HFC-32), or R410A (a near-azeotropic mixture of difluoromethane (HFC-32) and pentafluoroethane (HFC-125)), and combinations thereof and the working fluid has a miscibility range for HFC-32 and R410A of at least about −60° C. to about 50° C.