Working fluids comprising fluorinated olefins and polyol esters

Abstract

High viscosity working fluids comprising a fluorinated olefin refrigerant, such as a hydrofluoro-olefin refrigerant, and a high viscosity polyol ester comprising a select mixture of alkylcarboxy esters of pentaerythritol, di-pentaerythritol, tri-pentaerythritol and pentaerythritol oligomers are provided.

Claims

1. A working fluid comprising: i) a fluorinated olefin refrigerant, and ii) a polyol ester lubricant composition having a kinematic viscosity at 40 C. of from 150 to 360 cSt, which polyol ester lubricant composition comprises: a) from 25 to 40 wt % C.sub.5-12 alkylcarboxy esters of mono-pentaerythritol, b) from 15 to 25 wt % C.sub.5-12 alkylcarboxy esters of di-pentaerythritol, and c) from 40 to 55 wt % C.sub.5-12 alkylcarboxy esters of tri-pentaerythritol and higher pentaerythritol oligomers, wherein from 55 to 100 mol % of the alkylcarboxy groups are selected from C.sub.7-10 alkylcarboxy, and from 50 to 80 mol % of all alkylcarboxy groups are branched.

2. The working fluid according to claim 1 wherein 70 to 100 mol % of the alkylcarboxy groups are selected from C.sub.7-10 alkylcarboxy.

3. The working fluid according to claim 1 wherein 55 to 80 mol % of the alkylcarboxy groups are branched.

4. The working fluid according to claim 1 wherein from 28 to 39 wt % of the polyol ester lubricant composition consists of alkylcarboxy esters of mono-pentaerythritol.

5. The working fluid according to claim 1 wherein the polyol ester lubricant composition comprises: a) from 28 to 40 wt % C.sub.5-12 alkylcarboxy esters of mono-pentaerythritol, b) from 16 to 24 wt % C.sub.5-12 alkylcarboxy esters of di-pentaerythritol, and c) from 42 to 54 wt % C.sub.5-12 wt % alkylcarboxy esters of tri-pentaerythritol and higher pentaerythritol oligomers.

6. The working fluid according to claim 1 wherein 51 to 100% of the branched alkylcarboxy groups are 3,5,5-trimethylhexanoyl or 2,2,4,4-tetramethylbutanoyl.

7. The working fluid according to claim 1 wherein the polyol ester lubricant composition has a kinematic viscosity at 40 C. of at least 160 cSt.

8. The working fluid according to claim 1 wherein the polyol ester lubricant composition has a kinematic viscosity at 40 C. of from 194 to 340 cSt.

9. The working fluid according to claim 1 wherein fluorinated olefin refrigerant comprises a hydrofluoro- or perfluoro-olefin of from 2 to 7 carbon atoms.

10. The working fluid according to claim 9 wherein the hydrofluoro- or perfluoro-olefin contains three or more fluorine atoms.

11. The working fluid according to claim 10 wherein the hydrofluoro- or perfluoro-olefin contains four or more fluorine atoms.

12. The working fluid according to claim 10 wherein the hydrofluoro- or perfluoro-olefin comprises a pentafluoro-, tetrafluoro-, or trifluoro-propene isomer.

13. The working fluid according to claim 1 wherein fluorinated olefin refrigerant comprises a tetrafluoro-propene isomer.

14. The working fluid according to claim 1 wherein the fluorinated olefin refrigerant consists of hydrofluoro-olefins or perfluo-olefins.

15. The working fluid according to claim 1 wherein the fluorinated olefin refrigerant is a mixture comprising a hydrofluoro-olefin and/or perfluo-olefin, and a hydrocarbon, fluorinated alkyne, hydrofluoro-alkane and/or perfluoroalkane refrigerant.

16. The working fluid according to claim 15 wherein the fluorinated olefin refrigerant is a mixture comprising a hydrofluoro-olefin and a hydrofluoro-alkane.

Description

DETAILED DESCRIPTION

(1) The working fluid of the invention comprises i) a fluorinated olefin refrigerant, e.g., a hydrofluoro-olefin refrigerant, and ii) a particular high viscosity polyol ester lubricant composition.

(2) The polyol ester lubricant composition has a kinematic viscosity at 40 C. of from 190 to 360 cSt, e.g., from 190 to 340 cSt, and comprises a) from 25 to 40 wt % C.sub.5-12 alkylcarboxy esters of mono-pentaerythritol, b) from 15 to 25 wt % C.sub.5-12 alkylcarboxy esters of di-pentaerythritol, and c) from 40 to 55 wt % C.sub.5-12 alkylcarboxy esters of tri-pentaerythritol and higher pentaerythritol oligomers,
wherein from 55 to 100 mol % of the alkylcarboxy groups are selected from 07-10 alkylcarboxy, and from 50 to 80 mol % of all alkylcarboxy groups are branched. In many embodiments, 55 to 80 mol % of the alkylcarboxy groups are branched.

(3) In various embodiments, the polyol ester lubricant composition comprises, for example, a) from 28 to 40 wt %, e.g., from 30 to 40 wt % or from 33 to 40 alkylcarboxy esters of mono-pentaerythritol, b) from 15 to 25 wt %, 16 to 24 or 17 to 22 wt % alkylcarboxy esters of di-pentaerythritol, and c) from 40 to 54 wt %, 42 to 54 wt % or 40 to 50 wt % alkylcarboxy esters of tri-pentaerythritol and higher pentaerythritol oligomers.

(4) For example, in some embodiments the polyol ester lubricant composition comprises,

(5) a) from 25 to 40 wt % alkylcarboxy esters of mono-pentaerythritol,

(6) b) from 15 to 25 wt % alkylcarboxy esters of di-pentaerythritol, and

(7) c) from 40 to 55 wt % alkylcarboxy esters of tri-pentaerythritol and higher pentaerythritol oligomers.

(8) For example, in certain embodiments, e.g., at least 28, 29, 30, 31, 32, 33 or 34 wt % of the above alkylcarboxy esters are mono-pentaerythritol carboxy esters, and in some embodiments no more than 39, 38 or 37 wt % are mono-pentaerythritol carboxy esters;

(9) in certain embodiments e.g., at least 16, 17 or 18 wt %, of the above alkylcarboxy esters are di-pentaerythritol carboxy esters and in some embodiments no more than 23, 22 or 21 wt % are di-pentaerythritol carboxy esters; and

(10) in certain embodiments at least 40, 41 or 42 wt % of the above alkylcarboxy esters are esters of tri-pentaerythritol and higher pentaerythritol oligomers, and in some embodiments no more than 54, 53, 52, 51, 50 or 48 wt % are esters of tri-pentaerythritol and higher pentaerythritol oligomers.

(11) The alkylcarboxy groups are selected from C.sub.5-12 alkylcarboxy, for example from C.sub.5-10 alkylcarboxy, and at least 55 mol % are C.sub.7-10 alkylcarboxy, e.g., 55 to 100 mol %, 60 to 100 mol %, 70 to 100 mol %, 80 to 100 mol %, or 90 to 100 mol %, and in particular embodiments 50 mol %, 55 mol %, 60 mol %, 70 mol %, 75 mol %, 80 mol %, 85 mol %, 90 mol % or more are C.sub.8-10 alkylcarboxy.

(12) From 50 to 80 mol % of all alkylcarboxy groups in the polyol ester composition are branched. In many embodiments 55 to 80 mol % or 55 to 75 mol % of the alkylcarboxy groups are branched. Often, the branched alkylcarboxy groups are highly branched, e.g., they contain multiple branching sites and/or more than one group at a single site. For example, in certain embodiments, the majority, i.e., 51 to 100 mol % of the branched alkylcarboxy groups are 3,5,5-trimethylhexanoyl or 2,2,4,4-tetramethylbutanoyl, often 3,5,5-trimethylhexanoyl.

(13) The alkylcarboxy groups of the inventive polyol ester lubricant are mono-carboxylates, and less than 5 mol %, typically less than 2 mol %, and often none of the carboxylates are derived from di- or poly-carboxylic acids.

(14) The polyol ester lubricant composition of the inventive working fluid typically has a kinematic viscosity at 40 C. of at least 150, 160, 170, 180, 190 cSt or higher, e.g., at least 194 or at least 200 cSt. While there is no particular limit to how high the viscosity may be, in general the kinematic viscosity at 40 C. of the polyol ester composition reaches a useful upper limit of 400 cSt, but such fluids are difficult to work with, and in particular embodiments there is no reason to exceed 360 cSt or 340 cSt, and in many embodiments 320 or 325 cSt at 40 C. is sufficiently high in viscosity.

(15) The viscosity of the polyol ester lubricant in the presence of the refrigerant under the conditions of use is of primary concern, and this may be depressed by the amount of refrigerant dissolved therein. The instant polyol esters of the invention having the above viscosity differ from many similar polyolesters known in the art in that they do not generally dissolve so much hydrofluoro olefin refrigerant that the viscosity of the working fluid is unacceptably reduced, and therefore provide a working fluid with acceptable viscosity when blended with fluorinated olefin refrigerants and additives as typically found in the art.

(16) The mixture of polyol esters may be prepared by simple esterification of the appropriate pentaerythritol, dipentaerythritol, and poly(pentaerythritol)s, however this requires obtaining the individual polyols as starting materials. The polyol ester composition is more conveniently prepared by a two-step process analogous to that described in, e.g., U.S. Pat. Nos. 3,670,013, 6,444,626, 8,318,647 and the like.

(17) Other lubricants may be present in the working fluid, such as polyalphaolefins, polyalkylene glycols, alkylated aromatics, polyethers, mineral oils, phosphoric acid ester, other ester based lubricants, vegetable oils etc., however, the combination of polyol esters defined above is the majority lubricant component, typically comprising at least 80, 90, 95, or 98 wt % of the lubricant base stock, and in many embodiments, the polyol ester composition described above is the only lubricant in the inventive working fluid. Care must be used when adding other lubricant base stocks so that the desirable properties of the polyol ester composition relative to its use with hydrofluoro-olefins are not diminished.

(18) While other similar polyol esters possess a variety of useful properties, they do not typically exhibit the full complement of performance criteria, that is, both lubricating properties and fluoro-olefin miscibility, e.g., hydrofluoro-olefin miscibility, required for the present high viscosity working fluids.

(19) The highly fluorinated olefin refrigerants of the invention are known in the art, e.g., U.S. Published Patent Application No. 2012/0011864, and include E and Z isomers of, e.g.,

(20) 1,2,3,3,3-pentafluoro-1-propene; 1,1,3,3,3-pentafluoro-1-propene; 1,1,2,3,3-pentafluoro-1-propene; 1,2,3,3-tetrafluoro-1-propene; 2,3,3,3-tetrafluoro-1-propene; 1,3,3,3-tetrafluoro-1-propene; 1,1,2,3-tetrafluoro-1-propene; 1,1,3,3-tetrafluoro-1-propene; 1,2,3,3-tetrafluoro-1-propene; 3,3,3-trifluoro-1-propene; 2,3,3-trifluoro-1-propene; 1,1,2-trifluoro-1-propene; 1,2,3-trifluoro-1-propene; 1,1,3-trifluoro-1-propene; 1,3,3-trifluoro-1-propene;

(21) 1,1,1,2,4,4,4-heptafluoro-2-butene; 1,2,3,3,4,4,4-heptafluoro-1-butene; 1,1,1,2,3,4,4-heptafluoro-2-butene: 1,1,3,3,4,4,4-heptafluoro-1-butene; 1,1,2,3,4,4,4-heptafluoro-1-butene; 1,1,2,3,3,4,4-heptafluoro-1-butene; 2,3,3,4,4,4-hexafluoro-1-butene; 1,3,3,4,4,4-hexafluoro-1-butene; 1,2,3,4,4,4-hexafluoro-1-butene; 1,2,3,3,4,4-hexafluoro-1-butene; 1,1,2,3,4,4-hexafluoro-2-butene; 1,1,1,2,3,4-hexafluoro-2-butene; 1,1,1,2,4,4-hexafluoro-2-butene; 1,1,1,3,4,4-hexafluoro-2-butene; 1,1,2,3,3,4-hexafluoro-1-butene; 1,1,2,3,4,4-hexafluoro-1-butene; 1,1,1,2,4-pentafluoro-2-butene; 1,1,1,3,4-pentafluoro-2-butene; 3,3,4,4,4-pentafluoro-1-butene; 1,1,1,4,4-pentafluoro-2-butene; 1,1,1,2,3-pentafluoro-2-butene; 2,3,3,4,4-pentafluoro-1-butene; 1,1,2,4,4-pentafluoro-2-butene; 1,1,2,3,3-pentafluoro-1-butene; 1,1,2,3,4-pentafluoro-2-butene; 2,3,4,4,4-pentafluoro-1-butene; 1,2,4,4,4-pentafluoro-1-butene; 1,3,4,4,4-pentafluoro-1-butene; 1,3,3,4,4-pentafluoro-1-butene; 1,2,3,4,4-pentafluoro-1-butene; 3,3,4,4-tetrafluoro-1-butene; 1,1,1,2-tetrafluoro-2-butene; 1,1,1,3-tetrafluoro-2-butene;

(22) 3,3,3-trifluoro-2-(trifluoromethyl)-1-propene; 1,1-difluoro-2-(difluoromethyl)-1-propene; 1,3,3,3-tetrafluoro-2-methyl-1-propene; 3,3-difluoro-2-(difluoromethyl)-1-propene; 1,1,3,3,3-pentafluoro-2-methyl-1-propene; 2-(difluoromethyl)-3,3,3-trifluoro-1-propene; 1,3,3,3-tetrafluoro-2-(trifluoromethyl)-1-propene;

(23) 1,1,1,2,4,4,5,5,5-nonafluoro-2-pentene; 1,1,1,3,4,4,5,5,5-nonafluoro-2-pentene; 1,2,3,3,4,4,5,5,5-nonafluoro-1-pentene; 1,1,3,3,4,4,5,5,5-nonafluoro-1-pentene; 1,1,2,3,3,4,4,5,5-nonafluoro-1-pentene; 1,1,2,3,4,4,5,5,5-nonafluoro-2-pentene; 1,1,1,2,3,4,4,5,5-nonafluoro-2-pentene; 1,1,1,2,3,4,5,5,5-nonafluoro-2-pentene;

(24) 2,3,3,4,4,5,5,5-octafluoro-1-pentene; 1,2,3,3,4,4,5,5-octafluoro-1-pentene;

(25) 3,3,4,4,5,5,5-heptafluoro-1-pentene; 2,3,3,4,4,5,5-heptafluoro-1-pentene; 1,1,3,3,5,5,5-heptafluoro-1-pentene; 3,4,4,5,5,5-hexafluoro-2-pentene; 3,3,4,5,5,5-hexafluoro-1-pentene;

(26) 1,1,1,4,4,4-hexafluoro-2-(trifluoromethyl)-2-butene; 1,2,3,4,4,4-hexafluoro-3-(trifluoromethyl)-1-butene; 1,1,2,4,4,4-hexafluoro-3-(trifluoromethyl)-1-butene; 1,1,1,4,4,4-hexafluoro-2-(trifluoromethyl)-2-butene; 1,1,3,4,4,4-hexafluoro-3-(trifluoromethyl)-1-butene; 3,3,4,4,4-pentafluoro-2-(trifluoromethyl)-1-butene; 1,1,4,4,4-pentafluoro-3-(trifluoromethyl)-1-butene; 1,3,4,4,4-pentafluoro-3-(trifluoromethyl)-1-butene; 1,1,4,4,4-pentafluoro-2-(trifluoromethyl)-1-butene; 3,4,4,4-tetrafluoro-3-(trifluoromethyl)-1-butene; 1,1,1,2,4,4,4-heptafluoro-3-methyl-2-butene; 2,4,4,4-tetrafluoro-3-(trifluoromethyl)-1-butene; 1,4,4,4-tetrafluoro-3-(trifluoromethyl)-1-butene; 1,1,1,4-tetrafluoro-2-(trifluoromethyl)-2-butene; 1,1,1,3-tetrafluoro-2-(trifluoromethyl)-2-butene; 1,1,1-trifluoro-2-(trifluoromethyl)-2-butene; 1,1,1,4,4,4-hexafluoro-2-methyl-2-butene; 4,4,4-trifluoro-2-(trifluoromethyl)-1-butene;

(27) 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexene; 3,4,4,5,5,6,6,6-octafluoro-2-hexene; 3,3,4,4,5,5,6,6-octafluoro-1-hexene; 4,4,5,5,6,6,6-heptafluoro-2-hexene; 4,4,5,5,6,6,6-heptafluoro-1-hexene; 1,1,1,2,2,3,4-heptafluoro-3-hexene;

(28) 1,1,1,4,4,5,5,5-octafluoro-2-(trifluoromethyl)-2-pentene; 1,1,1,3,4,5,5,5-octafluoro-4-(trifluoromethyl)-2-pentene; 4,4,4-trifluoro-3,3-bis(trifluoromethyl)-1-butene; 1,1,1,4,4,4-hexafluoro-3-methyl-2-(trifluoromethyl)-2-butene; 2,3,3,5,5,5-hexafluoro-4-(trifluoromethyl)-1-pentene; 1,1,1,2,4,4,5,5,5-nonafluoro-3-methyl-2-pentene; 1,1,1,5,5,5-hexafluoro-4-(trifluoromethyl)-2-pentene; 1,1,1,4,4-pentafluoro-2-(trifluoromethyl)-2-pentene; 4,5,5,5-pentafluoro-2-(trifluoromethyl)-1-pentene; 3,3,4,4,5,5,5-heptafluoro-2-methyl-1-pentene;

(29) 4,5,5,5-tetrafluoro-4-(trifluoromethyl)-1-pentene; 1,1,1,2,5,5,5-heptafluoro-4-methyl-2-pentene;

(30) 1,1,1,3-tetrafluoro-2-(trifluoromethyl)-2-pentene; and the like;

(31) perfluorinated olefins include:

(32) 1,1,1,2,3,4,4,4-octafluoro-2-butene; 1,1,2,3,3,4,4,4-octafluoro-1-butene, 1,1,1,2,3,4,4,5,5,5-decafluoro-2-pentene; 1,1,2,3,3,4,4,5,5,5-decafluoro-1-pentene; 1,1,2,3,3,4,4,5,5,6,6,6-dodecafluoro-1-hexene; 1,1,1,2,2,3,4,5,5,6,6,6-dodecafluoro-3-hexene; 1,1,1,4,4,4-hexafluoro-2,3-bis(trifluoromethyl)-2-butene; 1,1,1,2,3,4,5,5,5-nonafluoro-4-(trifluoromethyl)-2-pentene; and the like.

(33) Often, the working fluid of the invention comprises a fluorinated or perfluorinated olefin of from 2 to 7 carbon atoms.

(34) In some embodiments of the invention, the refrigerant is entirely hydrofluoro-olef ins or perfluoro-olefins, for example, entirely hydrofluoro-olefins. In other embodiments, other known refrigerants are present, such as, hydrocarbon, fluorinated alkyne, hydrofluoro-alkane, perfluoroalkane or other halogenated refrigerants; carbon dioxide, ammonia and the like. Typically, the miscibility requirements of the lubricants with the fluorinated olefin of the invention can be met without the addition of solubility enhancers such as the perfluoro-ethers of U.S. Published Patent Application No. 2012/0011864.

(35) Generally, at least 20% by weight of the refrigerants present in the working fluids of the invention are hydrofluoro-olefins or perfluoro-olefins, typically hydrofluoro-olef ins; in some embodiments, 25 to 100 wt % are hydrofluoro-olefins or perfluoro-olefins. For example, in various embodiments of the invention, 25 to 75 wt %, 25 to 50 wt %, 50 to 100 wt %, 60 to 100 wt %, 75 to 100 wt %, 90 to 100 wt %, or 95 to 100 wt % of the refrigerants present in the working fluids of the invention are hydrofluoro-olefins or perfluoro-olefins.

(36) In many embodiments employing blends of fluorinated olefins with other refrigerants, the refrigerant is a blend of fluorinated olefins with other fluorinated refrigerants such as fluorinated alkynes, hydrofluoro-alkanes, perfluoro-alkanes, or with hydrocarbon refrigerants, for example, alkanes, alkenes and alkynes having from 1 to 5 carbon atoms.

(37) When adding other refrigerants along with the fluorinated olefins of the invention, care must be taken to ensure that miscibility and other desirable characteristics of the working fluid remain within useful parameters. For example, the alkane tetrafluoroethane and the olefin tetrafluoropropene are found in refrigerant blends, but the miscibility of each with high viscosity polyester lubricants are different and lubricants useful with one or the other may not be suitable with certain combinations of both together.

(38) For example, attempts were made to meet the miscibility and viscosity requirements, e.g., ISO 220 grade, using only esters formed from di-pentaerythritol and mixtures of branched C.sub.9 and linear C.sub.8 and C.sub.10 carboxylic acids, this viscosity could not be attained without including such a high amount of branched C.sub.9 acid that the lubricant became too miscible with the hydrofluoro-olefin refrigerant. That is, these di-pentaerythritol esters rely heavily on the branched acids to build viscosity, but the high level of branched acids needed to attain high-viscosity lubricants leads to oils that absorb to much refrigerant under operating conditions. Thus, the working fluid viscosity of highly branched POEs is often too low in the presence of HFO refrigerants.

(39) The use of oligomeric polyol esters blended with mono- and di-pentaerythritol esters may aid in obtaining high viscosity, but too much oligomeric material provides a lubricant that fails to work properly and exhibits cloudiness in miscibility tests. Further, after selecting an acceptable blend of mono-, di-, and oligomeric pentaerythritols to use as the polyol portion of the esters, it is found that only certain mixtures of carboxylates will provide the appropriate viscosity and miscibility with hydrofluoro-olefins for many demanding applications. For example, polyol esters with predominately C.sub.5 carboxylate groups are excluded from the present invention due to unsuitable miscibility with fluorinated olefins. The polyol esters of the inventive working fluids are therefore defined by at least the relative amounts of mono-, di-, and oligomeric pentaerythritol esters, the ratio of branched to linear carboxylates, and the required amount of 07-10 alkylcarboxylate.

(40) A series of polyol ester compositions were prepared for evaluation using standard industry tests for general effectiveness as a lubricant for mechanical devices, and also for effectiveness as a part of a working fluid containing R-1234ze. A sample of these comparative and inventive ester compositions are shown in Table 1, a fuller set of the lubricants are found in the Examples. In Table 1 the ratio of mono- to di- to tri- and higher pentaerythritol esters are reported as a weight % based on the total of polyol esters present in the composition as determined by gel permeation chromatography (GPC) and the carboxylate groups are reported in terms of the mole percent of each acid relative to the combined total moles of the carboxylic acids added during the esterification process. In the table, i-C5 represents a mixture of about 34% 2-methylbutanoic acid and 66% n-pentanoic acid; i-C9 represents 3,5,5-trimethylhexanoic acid; n-C8C10 represents a mixture primarily of n-octanoic and n-decanoic acid commercially available.

(41) TABLE-US-00001 TABLE 1 Kvis @ Mole % of Each Acid Pentaerythritol Polyol 40 C., cSt n-C5 i-C5 n-C7 i-C9 n-C8C10 Mono Di Tri & Higher Comp A 220 29 0 0 71 0 0 100 0 Comp I 220 0 0 50 0 50 25 19 56 Comp J 257 0 0 65 35 0 27 16 57 Comp L 220 0 30 70 0 0 22 12 65 INV 2 217 0 0 1 60 39 35 19 46 INV 3 215 0 0 1 65 34 37 19 44 INV 4 220 0 0 1 70 29 37 20 42 INV 6 320 0 0 1 65 34 30 17 53 INV 7 313 0 0 1 80 19 36 20 44

(42) It should be remembered that the relative amounts of polyol ester lubricant and R-1234ze refrigerant found in a working fluid in a heat transfer device can vary widely depending on the stage of the refrigeration cycle. For example, the working fluid can comprise from 1 to 99%, e.g., 2 to 98%, by weight of the polyol ester lubricant or from 1 to 99%, e.g., 2 to 98%, by weight of the refrigerant based on the combined weight of lubricant and refrigerant.

(43) The relative amounts reported for sealed tube miscibility testing in the examples or data tables herein of lubricant to refrigerant ratios refer to the amounts of each component that are charged initially to the apparatus being used.

(44) The miscibility of the lubricants of Table 1 with HFO was determined by using the industry standard sealed-tube method. Known quantities of lubricant and refrigerant were charged to a glass test tube. After sealing the open end of the tube, the liquid contents were visually observed while being slowly cooled and heated from about 60 C to about +70 C. It is common for lubricant-refrigerant combinations to exhibit both miscibility (only one homogeneous liquid phase present) and immiscibility (two liquid phases present) as the temperature changes. Generally, there is a low side miscibility limit below which the oil and lubricant separate into two distinct phases (an oil-rich phase and a lubricant-rich phase). Also, there may be a high-side miscibility limit above which the oil and lubricant separate into two phases. At temperatures between the high-side and low-side miscibility limits there exists a temperature range over which only one homogeneous liquid phase exists and it contains both oil and refrigerant.

(45) In Table 2 below, the temperatures of the low-side and high-side miscibility limits are reported for sealed tubes containing an overall composition that is 10% lubricant and 90% R-1234ze. This composition was chosen because for the inventive lubricants it has the narrowest miscibility range (high-side limit to low-side limit) and is representative of liquid phase local concentrations existing in refrigeration system heat exchangers (condenser and evaporator).

(46) Tests were also run to determine the impact of R-1234ze refrigerant on the properties of the lubricants in order to confirm the suitability of the inventive polyol ester lubricants in an R-1234ze-containing working fluid. The lubricant chosen for use with an R-1234ze refrigerant must not only be miscible with R-1234ze, but the lubricant must maintain adequate viscosity when refrigerant dissolves into it. The presence of R-1234ze in a lubricant is known to significantly lower its viscosity. The amount of refrigerant dissolved in the liquid phase was measured at representative conditions and is listed in the table below as refrigerant fraction. The viscosity of the resulting lubricant-refrigerant liquid is called the diluted viscosity or working viscosity and is a function of temperature, pressure and the solubility of the refrigerant in the lubricant. The combination of properties (good miscibility, low solubility, high viscosity) is vital to an R-1234ze working fluid and is difficult to attain.

(47) The viscosity and composition of lubricant/R-1234ze mixtures as a function of temperature and pressure were measured using a temperature controlled circulation loop apparatus comprising a pump, mass flow/density meter, high pressure viscometer, lubricant/refrigerant reservoir and pressure transducer. Details of the procedures and apparatus are found in the experimental section of the application. Measurements were collected in the temperature range from 10 C. to 120 C. and compositions of R-1234ze in lubricant from 0 to about 35 wt %. Refrigerant fraction and diluted viscosity data in Table 2 were obtained under temperature and pressures commonly encountered by HFO working fluids in commercial applications. Compositions of the invention exhibit acceptable viscosity over the range of temperatures and pressures describing the operating window of the system.

(48) TABLE-US-00002 TABLE 2 Sealed Tube Test Working Fluid Viscosity 10% Oil in Refrigerant and Composition at Low Side High Side Representative Conditions Miscibility Miscibility Refrigerant Diluted Limit Limit Fraction Viscosity Comp A <62 C. >70 C. 34.7 wt % 3.3 cSt Comp I NM NM 30.1 wt % 7.6 cSt Comp J 13 C. 51 C. Comp L 15 C. 32 C. 32.1 wt % 5.7 cSt INV 2 12 C. 71 C. 32.5 wt % 4.6 cSt INV 3 27 C. 72 C. INV 4 41 C. 73 C. INV 7 44 C. 72 C. 32.8 wt % 4.7 cSt INV 6 8 C. 64 C. 31.9 wt % 5.7 cSt N.M. = Not miscible over the temperature range observed

(49) Comparative Example A exhibits excellent miscibility over a wide temperature range, but this composition has an unacceptably low diluted viscosity under representative compressor operating conditions. Comparative Example I has an acceptable diluted viscosity, but is not useful due to it being immiscible with R-1234ze. Comparative examples L and J have acceptable low-side miscibility limits but are not sufficiently miscible at higher temperatures, separating at 32 and 51 C. Inventive examples are miscible with R-1234ze over an acceptable temperature range, exhibit acceptable diluted viscosities, and have less affinity for the refrigerant than a traditional high viscosity ester such as Comparative Example A.

(50) Not wanting to be bound by theory, it is believed that maintaining miscibility below temperatures of 60 C. may correlate generally with overly high refrigerant fraction and an undesirably low diluted viscosity as shown here for Comparative Example A. Such working fluids are unsuitable for the present invention, wherein the lubricants typically have a low end miscibility limit of from 1 to 55 C., and typically from 1 to 45 C. for an composition that is 10% lubricant and 90% R-1234ze measured as described above.

(51) The polyol ester compositions of the invention thus demonstrate a superior combination of physical properties and performance characteristics and are ideally suited for use with R-1234ze in heat transfer working fluids.

(52) Common additives which may also be present in the working fluid include antioxidants, extreme-pressure additives, antiwear additives, friction reducing additives, defoaming agents, profoaming agents, metal deactivators, acid scavengers and the like.

(53) Examples of antioxidants that can be used include phenolic antioxidants such as 2,6-di-t-butyl-4-methylphenol and 4,4-methylenebis(2,6-di-t-butylphenol); amine antioxidants such as p,p-dioctylphenylamine, monooctyldiphenylamine, phenothiazine, 3,7-dioctylphenothiazine, phenyl-1-naphthylamine, phenyl-2-naphthylamine, alkylphenyl-1-naphthylamine, and alkylphenyl-2-naphthylamine; sulfur-containing antioxidants such as alkyl disulfide, thiodipropionic acid esters and benzothiazole; and zinc dialkyl dithiophosphate and zinc diaryl dithiophosphate.

(54) Examples of extreme-pressure additives, antiwear additives, friction reducing additives that can be used include zinc compounds such as zinc dialkyl dithiophosphate and zinc diaryl dithiophosphate; sulfur compounds such as thiodipropinoic acid esters, dialkyl sulfide, dibenzyl sulfide, dialkyl polysulfide, alkylmercaptan, dibenzothiophene and 2,2-dithiobis(benzothiazole); sulfur/nitrogen ashless antiwear additives such as dialkyldimercaptothiadiazoles and methylenebis(N,N-dialkyldithiocarbamates); phosphorus compounds such as triaryl phosphates such as tricresyl phosphate and trialkyl phosphates; dialkyl or diaryl phosphates; trialkyl or triaryl phosphites; amine salts of alkyl and dialkylphosphoric acid esters such as the dodecylamine salt of dimethylphosphoric acid ester; dialkyl or diaryl phosphites; monoalkyl or monoaryl phosphites; fluorine compounds such as perfluoroalkyl polyethers, trifluorochloroethylene polymers and graphite fluoride; silicon compounds such as a fatty acid-modified silicone; molybdenum disulfide, graphite, and the like. Examples of organic friction modifiers include long chain fatty amines and glycerol esters.

(55) Examples of defoaming and profoaming agents that can be used include silicone oils such as dimethylpolysiloxane and organosilicates such as diethyl silicate. Examples of the metal deactivators that can be used include benzotriazole, tolyltriazole, alizarin, quinizarin and mercaptobenzothiazole. Furthermore, epoxy compounds such as phenyl glycidyl ethers, alkyl glycidyl ethers, alkylglycidyl esters, epoxystearic acid esters and epoxidized vegetable oil, organotin compounds and boron compounds may be added as acid scavengers or stabilizers.

(56) Examples of moisture scavengers include trialkylorthoformates such as trimethylorthoformate and triethylorthoformate, ketals such as 1,3-dioxacyclopentane, and amino ketals such as 2,2-dialkyloxazolidines.

(57) The working fluids comprising the present polyol esters and refrigerant can be used in a wide variety of refrigeration and heat energy transfer applications. Non-limiting examples include all ranges of air conditioning equipment from small window air conditioners, centralized home air conditioning units to light industrial air conditioners and large industrial units for factories, office buildings, apartment buildings and warehouses. Refrigeration applications include small home appliances such as home refrigerators, freezers, water coolers, vending machines and icemakers to large scale refrigerated warehouses and ice skating rinks. Also included in industrial applications would be cascade grocery store refrigeration and freezer systems. Heat energy transfer applications include heat pumps for house hold heating and hot water heaters. Transportation related applications include automotive and truck air conditioning, refrigerated semi-trailers as well as refrigerated marine and rail shipping containers.

EXAMPLES

(58) The viscosity and composition of lubricant/R-1234ze mixtures as a function of temperature and pressure were measured using a temperature controlled circulation loop apparatus comprising a pump, mass flow/density meter, high pressure viscometer, lubricant/refrigerant reservoir and pressure transducer. Thermocouples are located at multiple locations in the loop as well as directly in the mass flow meter and viscometer. The design of the loop allows for continuous circulation of the liquid mixture as well as providing agitation to achieve rapid vapor-liquid equilibrium.

(59) The lubricant was first charged to the system gravimetrically, the circulation loop was cooled to 10 C. and then the R-1234ze was charged gravimetrically in an amount necessary to achieve the desired overall R-1234ze/lubricant composition. For safety reasons the loop was not filled to capacity and a small vapor space existed at the top of the bulk reservoir, and a vapor space correction was applied to the composition to account for R-1234ze in the vapor phase. After charging, a gear pump circulated the liquid through the measurement devices. Bulk mixture pressure, liquid density, temperature, and viscosity were measured as the entire circulation loop was heated and cooled over the range of about 120 C. to 10 C.

(60) Ester Compositions

(61) The following polyol ester compositions were prepared using above cited methods. The ratio of mono- to di- to tri- and higher pentaerythritol esters are reported as a weight % of all such esters as determined by GPC and the carboxylate groups are reported in terms of mole % of each acid added to the esterification process based on total moles of acid used; i-C.sub.5 is an industrial chemical product called isopentanoic acid which is a mixture of about 34% 2-methylbutanoic acid and 66% n-pentanoic acid; i-C9 is 3,5,5-trimethylhexanoic acid, known industrially as isononanoic acid; n-C8C10 is an industrial chemical product that is a mixture primarily of n-octanoic and n-decanoic acid and is commercially available from e.g., Proctor and Gamble Chemicals, as C-810 (NA).

(62) TABLE-US-00003 Polyol Ester Compositions Viscosity Mole % of Each Acid Wt % Pentaerythritol cSt @ Based on Total Moles Acid Polyol Example 40 C. n-C5 i-C5 n-C7 i-C9 n-C8 C10 Mono Di Tri & Higher Comp A ~220 29 0 0 71 0 0 100 0 Comp B 400 0 0 0 100 0 0 100 0 Comp C 170 0 0 17 68 15 0 100 0 INV 1 195 0 0 1 55 44 35 18 46 INV 2 217 0 0 1 60 39 35 19 46 INV 3 215 0 0 1 65 34 37 19 44 INV 4 ~220 0 0 1 70 29 37 20 42 Comp D 244 0 0 0 80 20 42 21 37 Comp E 233 0 50 0 50 0 35 20 45 Comp F 220 0 20 1 20 59 25 16 59 Comp G 189 0 30 1 30 39 29 17 54 Comp H 226 0 30 20 30 20 26 17 58 INV 5 233 0 0 50 50 0 30 17 53 Comp I ~220 0 0 50 0 50 25 19 56 Comp J 257 0 0 65 35 0 27 16 57 Comp K 205 0 40 60 0 0 22 13 65 Comp L ~220 0 30 70 0 0 22 12 65 INV 6 320 0 0 1 65 34 30 17 53 INV 7 313 0 0 1 80 19 36 20 44 Comp M 346 0 0 1 90 9 39 20 42

(63) The following table lists the mol % of branched carboxylates of the above polyol esters, based on total moles of carboxylic acid used in the esterification, and shows the low and high side miscibility limits of 10% of the polyol ester in R-1234ze.

(64) TABLE-US-00004 Miscibility of 10% Polyol Ester Compositions in R-1234ze. Carboxylate Miscibility Kvis Mol % Mol % Pentaerythritol Low High 40 C. C7-C10 Branched Mono/Di/Tri and Side Side Example cSt Carboxylate Carboxylate Higher wt % Limit Limit Comp A ~220 71 71 0/100/0 <62 C. >70 C. Comp B 400 100 100 0/100/0 65 C. 70 C. Comp C 170 100 68 0/100/0 65 C. 70 C. INV 1 195 100 55 35/18/46 9 C. 60 C. INV 2 217 100 60 35/19/46 12 C. 71 C. INV 3 215 100 65 37/19/44 27 C. 72 C. INV 4 ~220 100 70 37/20/42 41 C. 73 C. Comp D 244 100 80 42/21/37 60 C. 73 C. Comp E 233 50 50 35/20/45 60 C. 72 C. Comp F 220 80 27 25/16/59 NM NM Comp G 189 70 40 29/17/54 7 C. 46 C. Comp H 226 70 40 26/17/58 29 C. 55 C. INV 5 233 100 50 30/17/53 43 C. 74 C. Comp I ~220 100 0 25/19/56 N.M. N.M. Comp J 257 100 35 27/16/57 13 C. 51 C. Comp K 205 60 14 22/13/65 36 C. 44 C. Comp L ~220 70 10 22/12/65 15 C. 32 C. INV 6 320 100 65 30/17/53 8 C. 64 C. INV 7 313 100 80 36/20/44 44 C. 72 C. Comp M 346 100 90 39/20/42 62 C. 72 C. N.M. = Not miscible over the temperature range observed

(65) Each inventive lubricant comprises from 25 to 40 wt % mono-pentaerythritol estes; from 15 to 25 wt % di-pentaerythritol esters; from 40 to 55 wt % tri-pentaerythritol and higher pentaerythritol esters, 55-100% C.sub.7-10 alkylcarboxylates, 50-80% of all alkylcarboxylates are branched and exhibit a low end miscibility limit for 10 wt % of polyol ester in R-1234ze of from 1 to 45 C.