Polyol ester lubricants for hermetically sealed refrigerating compressors

Abstract

A high quality lubricant for hermetically sealed domestic air conditioner and refrigerator compressors, especially those using chlorine free hydrofluorocarbon refrigerant working fluids, is provided by mixed esters of hindered polyols, most desirably pentaerythritol, with a mixture of carboxylic acids including at least some iso-pentanoic acid along with either or both of iso-nonanoic acid and dibasic acids such as adipic.

The invention claimed is:  
     
         1 . A composition of matter suitable for serving as a lubricant or lubricant base stock, said composition being a liquid with a viscosity between about 22.5 and about 44 centistokes at 40° C. and consisting essentially of a mixture of polyol ester molecules in which at least about 92% of the alcohol moieties are selected from the group consisting of the alcohol moieties derived from TMP, DTMP, PE, and DPE and at least about 92% of the acyl groups are selected from the group consisting of the acyl groups of all the straight and branched chain monobasic and dibasic carboxylic acids with from four to twelve carbon atoms each, said alcohol moieties and acyl groups being further selected subject to the constraints that (a) a total of at least about 3% of the acyl groups in the mixture are acyl groups of i-C 5  acid; (b) the ratio of the % of acyl groups in the mixture that contain 8 or more carbon atoms and are unbranched to the % of acyl groups in the mixture that are both branched and contain not more than six carbon atoms is not greater than about 1.56; (c) the % of acyl groups in the mixture that contain at least nine carbon atoms, whether branched or not, is not greater than about 81; and (d) not more than about 2% of the acyl groups in the ester mixture are part of acid molecules with more than two carboxyl groups each; and either (d)(1) a total of at least about 20% of the acid molecules in the mixture are one of the trimethylhexanoic acids; at least about 90% of the alcohol moieties in the esters are those of PE; and not more than about 7.5% of the acyl groups in the ester mixture are dibasic; or (d)(2) at least about 2.0%, but not more than about 13% of the acyl groups in the ester mixture are dibasic; and a total of at least about 82% of the monobasic acyl groups in the acid mixture have either five or six carbon atoms each.  
     
     
         2 . A composition according to    claim 1   , with a viscosity between about 25.0 and about 38.5 centistokes at 40° C. and consisting essentially of a mixture of polyol ester molecules in which the alcohol moieties and acyl groups are selected subject to the constraints that (a) a total of at least about 7% of the acyl groups in the mixture are acyl groups of i-C 5  acid; (b) the ratio of the % of acyl groups in the mixture that contain 8 or more carbon atoms and are unbranched to the % of acyl groups in the mixture that are both branched and contain not more than six carbon atoms is not greater than about 1.56; (c) the % of acyl groups in the mixture that contain at least nine carbon atoms, whether branched or not, is not greater than about 67; and either (d)(1) a total of at least about 29% of the acyl groups in the mixture are in one of the trimethylhexanoic acids and not more than about 6.0% of the acyl groups in the acid mixture are dibasic; or (d)(2) at least about 2.8%, but not more than about 10%, of the acyl groups in the ester mixture are dibasic and a total of at least about 85% of the monobasic acyl groups in the ester mixture have either five or six carbon atoms each.  
     
     
         3 . A composition according to    claim 2    with a viscosity between about 27.4 and about 36.6 centistokes at 40° C. and consisting essentially of a mixture of polyol ester molecules in which at least about 95% of the alcohol moieties are selected from the group consisting of the alcohol moieties derived from TMP, DTMP, PE, and DPE and at least about 95% of the acyl groups are selected from the group consisting of the acyl groups of all the straight and branched chain monobasic and dibasic carboxylic acids with from four to twelve carbon atoms each, said alcohol moieties and acyl groups being further selected subject to the constraints that (a) a total of at least about 10% of the acyl groups in the mixture are acyl groups of i-C 5  acid; (b) the ratio of the % of acyl groups in the mixture that contain 8 or more carbon atoms and are unbranched to the % of acyl groups in the mixture that are both branched and contain not more than six carbon atoms is not greater than about 1.21; (c) the % of acyl groups in the mixture that contain at least nine carbon atoms, whether branched or not, is not greater than about 67; and (d) not more than 1% of the acyl groups in the esters contain more than two carboxyl groups each; and either (d)(1) a total of at least about 35% of the acid molecules in the mixture are one of the trimethylhexanoic acids and not more than about 3% of the acyl groups in the ester mixture are dibasic; or (d)(2) at least about 3.6% of the acyl groups in the ester mixture are dibasic; and a total of at least about 93% of the monobasic acyl groups in the acid mixture have five carbon atoms each.  
     
     
         4 . A composition according to    claim 3    with a viscosity between about 28.5 and about 36.6 centistokes at 40° C. and consisting essentially of a mixture of polyol ester molecules in which the alcohol moieties and acyl groups are selected subject to the constraints that (a) a total of at least about 14% of the acyl groups in the mixture are acyl groups of i-C 5  acid; (b) the ratio of the % of acyl groups in the mixture that contain 8 or more carbon atoms and are unbranched to the % of acyl groups in the mixture that are both branched and contain not more than six carbon atoms is not greater than 1.00; (c) the % of acyl groups in the mixture that contain at least nine carbon atoms, whether branched or not, is not greater than about 49; and (d) not more than 0.4% of the acyl groups in the ester mixture contain more than two carboxyl groups each; and either (d)(1) a total of at least about 35% of the acyl groups in the mixture are one of the trimethylhexanoic acids and at least about 29% of the acyl groups in the mixture are 3,5,5-trimethylhexanoyl groups; at least about 95% of the alcohol moieties in the esters are those of PE; and not more than about 1.7% of the acyl groups in the ester mixture are dibasic; or (d)(2) at least about 4.1% of the acyl groups in the ester mixture are dibasic and contain from five to seven carbon atoms each and a total of at least about 96% of the monobasic acyl groups in the acid mixture have five carbon atoms each.  
     
     
         5 . A composition according to    claim 4    with a viscosity between about 29.4 and about 35.7 centistokes at 40° C. and consisting essentially of a mixture of polyol ester molecules in which at least about 95% of the acyl groups are selected from the group consisting of the acyl groups of all the straight and branched chain monobasic and dibasic carboxylic acids with from four to twelve carbon atoms each and the alcohol moieties and acyl groups are selected subject to the constraints that (a) a total of at least 16% of the acyl groups in the ester mixture are acyl groups of i-C 5  acid; (b) the ratio of the % of acyl groups in the mixture that contain 8 or more carbon atoms and are unbranched to the % of acyl groups in the mixture that are both branched and contain not more than five carbon atoms is not greater than about 1.00; (c) the % of acyl groups in the mixture that contain at least nine carbon atoms, whether branched or not, is not greater than about 49; and (d) at least about 95% of the alcohol moieties in the esters are those of PE, and either (d)(1) a total of at least about 41% of the acyl groups in the ester mixture are acyl groups of one of the trimethylhexanoic acids and at least about 29% of the acyl groups in the mixture are 3,5,5-trimethylhexanoyl groups; and not more than 1% of the acyl groups in the ester mixture are dibasic; or (d)(2) at least 4.9% of the acyl groups in the ester mixture are dibasic.  
     
     
         6 . A compounded lubricant consisting essentially of at least about 95% by weight of a composition according to    claim 5    and a balance of one or more additives selected from the group consisting of oxidation resistance and thermal stability improvers, corrosion inhibitors, metal deactivators, lubricity additives, viscosity index improvers, pour and floc point depressants, detergents, dispersants, antifoaming agents, anti-wear agents, and extreme pressure resistant additives.  
     
     
         7 . A compounded lubricant consisting essentially of at least about 92% by weight of a composition according to    claim 3    and a balance of one or more additives selected from the group consisting of oxidation resistance and thermal stability improvers, corrosion inhibitors, metal deactivators, lubricity additives, viscosity index improvers, pour and floc point depressants, detergents, dispersants, antifoaming agents, anti-wear agents, and extreme pressure resistant additives.  
     
     
         8 . A compounded lubricant consisting essentially of at least about 92% by weight of a composition according to    claim 2    and a balance of one or more additives selected from the group consisting of oxidation resistance and thermal stability improvers, corrosion inhibitors, metal deactivators, lubricity additives, viscosity index improvers, pour and floc point depressants, detergents, dispersants, antifoaming agents, anti-wear agents, and extreme pressure resistant additives.  
     
     
         9 . A compounded lubricant consisting essentially of at least about 92% by weight of a composition according to    claim 1    and a balance of one or more additives selected from the group consisting of oxidation resistance and thermal stability improvers, corrosion inhibitors, metal deactivators, lubricity additives, viscosity index improvers, pour and floc point depressants, detergents, dispersants, antifoaming agents, anti-wear agents, and extreme pressure resistant additives.  
     
     
         10 . A refrigerant working fluid consisting essentially of at least 85% by weight of a primary heat transfer fluid selected from the group consisting of pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluroethane, tetrafluoroethanes, and mixtures thereof and a balance of a lubricant according to    claim 9   .  
     
     
         11 . A refrigerant working fluid consisting essentially of at least 85% by weight of a primary heat transfer fluid selected from the group consisting of pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluroethane, tetrafluoroethanes, and mixtures thereof and a balance of a lubricant according to    claim 8   .  
     
     
         12 . A refrigerant working fluid consisting essentially of at least 85% by weight of a primary heat transfer fluid selected from the group consisting of pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluroethane, tetrafluoroethanes, and mixtures thereof and a balance of a lubricant according to    claim 7   .  
     
     
         13 . A refrigerant working fluid consisting essentially of at least 85% by weight of 1,1,1,2-tetrafluroethane and a balance of a lubricant according to    claim 6   .  
     
     
         14 . A refrigerant working fluid consisting essentially of at least 85% by weight of a primary heat transfer fluid selected from the group consisting of pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluroethane, tetrafluoroethanes, and mixtures thereof and a balance of a lubricant according to    claim 5   .  
     
     
         15 . A refrigerant working fluid consisting essentially of at least 85% by weight of a primary heat transfer fluid selected from the group consisting of pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluroethane, tetrafluoroethanes, and mixtures thereof and a balance of a lubricant according to    claim 4   .  
     
     
         16 . A refrigerant working fluid consisting essentially of at least 85% by weight of a primary heat transfer fluid selected from the group consisting of pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluroethane, tetrafluoroethanes, and mixtures thereof and a balance of a lubricant according to    claim 3   .  
     
     
         17 . A refrigerant working fluid consisting essentially of at least 85% by weight of a primary heat transfer fluid selected from the group consisting of pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluroethane, tetrafluoroethanes, and mixtures thereof and a balance of a lubricant according to    claim 2   .  
     
     
         18 . A refrigerant working fluid consisting essentially of at least 85% by weight of a primary heat transfer fluid selected from the group consisting of pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluroethane, tetrafluoroethanes, and mixtures thereof and a balance of a lubricant according to    claim 1   .  
     
     
         19 . A process for operating a refrigerator comprising cyclic compression, liquefaction, expansion, and evaporation of a heat transfer fluid, said heat transfer fluid consisting essentially of at least 85% by weight of 1,1,1,2-tetrafluoroethane and a balance of a lubricant according to    claim 6   .  
     
     
         20 . A process for operating a refrigerator comprising cyclic compression, liquefaction, expansion, and evaporation of a heat transfer fluid, said heat transfer fluid consisting essentially of at least 85% by weight of a primary heat transfer fluid selected from the group consisting of pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluroethane, tetrafluoroethanes, and mixtures thereof and a balance of a lubricant according to    claim 1   .