Polyol ester lubricants with active Anti-wear additive for refrigeration applications

Abstract

Lubricant compositions comprising at least 85wt% of a polyolester; 0.1 to 1wt% of at least one dithiodialkylphosphoric acid ester; 0.075 to 0.3wt% of at least one triazole compound; and 0.075 to 0.3wt% of at least one phenol-based antioxidant. Methods of improving stability in a heat transfer system charged with a lubricant composition comprising at least 85wt% of a polyolester, the method comprising, adding to the lubricant composition an additive composition comprising: a) 0.1 to 1wt% of at least one dithiodialkylphosphoric acid ester; b) 0.075 to 0.3wt% of at least one triazole compound; and c) 0.075 to 0.3wt% of at least one phenol-based antioxidant.

Description

POLYOL ESTER LUBRICANTS WITH ACTIVE ANTI- WEAR ADDITIVE FOR REFRIGERATION APPLICATIONS***FIELD OF THE INVENTION

[0001] The disclosed technology relates to polyolester lubricant compositions with sulfur-containing phosphorous anti-wear agents for use in heat transfer systems with fluorinated refrigerants.BACKGROUND OF THE INVENTION

[0002] Heat transfer system lubricants of polyolesters are usually additized with phosphate esters to improve the lubricant wear and durability. In certain instances, depending on the heat transfer system design or the refrigerant used, severe wear issues cannot be overcome by the use of phosphate esters alone as anti-wear agents. In such cases, there is a need to use a more active and effective lubricant additive package that can improve severe wear issues without impacting other requirements of the heat transfer system. One of the major considerations of an additive package is the chemical reactivity of the additive package with other chemistries in the base oil and the refrigerant. Chemical interactions between other lubricant additives or the refrigerant can yield solids or other corrosive soluble species at high temperatures that are detrimental to the integrity and durability of the heat transfer system’s metal components.

[0003] Thus, there is a need for a heat transfer lubricant capable of resolving severe wear issues that is not reactive with other additive components, the refrigerant, or the heat transfer system’s metal components.SUMMARY OF THE INVENTION

[0004] The disclosed technology, therefore, solves the problem of improving the antiwear and extreme pressure properties, or stability of a lubricant for a heat transfer system. The disclosed technology provides for a lubricant composition that is an ISO 32 polyolester with sulfur-containing phosphorous anti-wear agents. The lubricant composition works well with fluorinated refrigerants, for example, R-404A. Accordingly, lubricant compositions for use with fluorinated refrigerants are disclosed herein.

[0005] The disclosed lubricant compositions may comprise: at least 85wt% of a polyolester; 0.1 to lwt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%) of at least one dithiodialkylphosphoric acid ester; 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one triazole compound; and 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one phenol-based antioxidant.

[0006] The lubricant compositions may be used with fluorinated refrigerants comprising at least 30wt% or 50wt% of a polyfluorinated hydrocarbon containing 1 to 6 or 2 to 6 carbon atoms. In some embodiments, all the carbon bonds are saturated.

[0007] In some embodiments, the polyolester comprises at least one polyol that may be esterified with at least one linear or branched hydrocarbyl acid having 4 to 12 carbon atoms. In some embodiments, the at least one linear or branched hydrocarbyl acid may be a Cs linear hydrocarbyl acid, a C7 linear hydrocarbyl acid, a C9 branched hydrocarbyl acid, or combinations thereof. In yet other embodiments, the at least one polyol may be trimethylolpropane, pentaerythritol, or combinations thereof.

[0008] In some embodiments, the lubricant composition may comprise at least one dithiodialkylphosphoric acid ester that has at least one alkyl group of 3 to 8 carbon atoms. In other embodiments, the at least one dithiodialkylphosphoric acid ester may have at least two alkyl groups of 3 to 8 carbon atoms.

[0009] In some embodiments, the dithiodialkylphosphoric acid ester may be represented by the formula: s ..R’O - P - SR--OR1wherein each R1may independently be a linear or branched alkyl group containing 3 to 8 carbon atoms; and R2may be a hydrocarbyl group containing 2 to 12 carbon atoms or an acylated hydrocarbyl group containing 3 to 12 carbon atoms.

[0010] In yet other embodiments, the dithiodialkylphosphoric acid ester may be represented by the formula:wherein each R1may independently be a linear or branched alkyl group containing 3 to 8 carbon atoms; and R3may be a hydrocarbyl group containing 1 to 6 carbon atoms.

[0011] In some embodiments, the dithiodialkylphosphoric acid ester may present in an amount to provide 600 ppm to 1200 ppm phosphorus by mass to the lubricant composition.

[0012] In some embodiments, the lubricant composition may comprise at least one triazole compound that is an alkyl-substituted triazole, an aryl -substituted triazole, or mixtures thereof. In yet other embodiments, the least one triazole compound may be a benzotriazole compound. Exemplary benzotriazole compounds include benzotri azoles represented by the formula:wherein R is hydrogen or a hydrocarbyl group of 1 to 6 carbon atoms.

[0013] In some embodiments, the lubricant composition may comprise at least one phenol -based antioxidant comprising 2,6-di-t-butylphenol, a substituted a 2,6-di-t-bu- tylphenol, or combinations thereof. In yet other embodiments, the phenol-based antioxidant may be butylated hydroxytoluene (BHT) or butylated hydroxyanisol (BHA), or combinations thereof. In some embodiments, the lubricant composition may be free or substantially free of diarylamine compounds, for example N,N’-dinonylated diphenylamine.

[0014] In some embodiments, the lubricant compositions may be used with fluorinated refrigerants comprising at least 30wt% or 50wt% of a polyfluorinated hydrocarbon containing 1 to 6 or 2 to 6 carbon atoms. In some embodiments, all the carbon bonds are saturated. In some embodiments the lubricant composition may be used with a fluorinated refrigerant comprising a polyfluorinated hydrocarbon that is a fluorinated olefin containing 2 to 5 carbon atoms. In the same or other embodiments, the polyfluorinated hydrocarbon of the fluorinated refrigerant may contain 2 to 6 fluorine atoms. In yet other embodiments, the fluorinated refrigerant may further comprise at least 10wt% fluorinated methane or a fluorinated alkene containing 2 to 4 carbon atoms, for example polyfluorinated propene. In some embodiments, the refrigerant contains both fluorinated methane and a fluorinated alkene. In some embodiments, the fluorinated refrigerant may comprise at least 50wt% 2, 3, 3, 3 -tetrafluoro-propene and 10wt% to 30wt% difluoromethane. In yet other embodiments, the fluorinated refrigerant may further comprise up to 7wt% carbon dioxide.

[0015] The disclosed lubricant compositions are suitable for use in heat transfer equipment and systems. Accordingly, a heat transfer system charged with the lubricant composition as described above is disclosed. Exemplary heat transfer systems include,but are not limited to, heat pump systems, refrigeration systems, and air-conditioning systems.

[0016] Methods of improving stability in a heat transfer system charged with a lubricant composition comprising at least 85wt% of a polyolester are also disclosed. The methods may comprise, adding to the lubricant composition an additive composition comprising: 0.1 to lwt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%) of at least one dithiodialkylphosphoric acid ester; 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one triazole compound; and 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one phenol-based antioxidant. The improvement in stability may be measured using the ASHRAE 97 standard test.

[0017] In other embodiments, methods of improving the extreme pressure properties of a lubricant composition comprising at least 85wt% of a polyolester are disclosed. The methods may comprise, adding to the lubricant composition an additive composition comprising: 0.1 to lwt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%) of at least one dithiodialkylphosphoric acid ester; 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one triazole compound; and 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one phenol-based antioxidant. The improvement to the extreme pressure properties of the lubricant composition may be measured using the ASTM D3233 standard test.

[0018] The uses of an additive composition to improve stability in a heat transfer system charged with a lubricant composition or improve the extreme pressure properties of a lubricant composition are disclosed. The additive composition may comprise: 0.1 to lwt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%) of at least one dithiodialkylphosphoric acid ester; 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one triazole compound; and 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one phenol -based antioxidant. The improvement in stability may be measured using the ASHRAE 97 standard test. The improvement in extreme pressure properties may be measured using the ASTM D3233 standard test.DETAILED DESCRIPTION OF THE INVENTION

[0019] Various preferred features and embodiments will be described below by way of non-limiting illustration. Lubricant compositions for use with fluorinated refrigerants are disclosed herein. The disclosed lubricant compositions may comprise: at least 85wt% of a polyolester; 0.1 to lwt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%) of at least one dithiodialkylphosphoric acid ester; 0.075 to 0.3wt% (or 0.08 to0.2wt%, or 0.1 to 0.2wt%) of at least one triazole compound; and 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one phenol-based antioxidant.Polyolester

[0020] Suitable polyolesters (or “POE”) are not overly limited and may include a polyol esterified with at least one (mono)carboxylic acid that has at least 4 carbon atoms. In yet other embodiments, the polyolester oil comprises a polyol esterified with a mixture of (mono)carboxylic acids or their anhydrides, wherein the (mono)carboxylic acids or anhydrides, individually, have 4 to 13 carbon atoms. Suitable ratios of the C4 to C13 carboxylic acids or anhydrides include but are not limited to 95:5 to 5:95. In yet other embodiments the mixture of (mono)carboxylic acids or their anhydrides comprises at least three C4 to C13 carboxylic acid or anhydrides.

[0021] In yet other embodiments, the polyolester comprises at least one polyol that may be esterified with at least one linear or branched hydrocarbyl acid having 4 to 12 carbon atoms. In some embodiments, the at least one linear or branched hydrocarbyl acid may be a C5 linear hydrocarbyl acid, a C7 linear hydrocarbyl acid, a C9 branched hydrocarbyl acid, or combinations thereof.

[0022] As used herein, the term “hydrocarbyl” refers to a group having a carbon atom directly attached to the remainder of the molecule, where the group includes at least carbon and hydrogen atoms. If the hydrocarbyl group comprises more than one carbon atom, then those carbons need not necessarily be linked to each other. For example, at least two of the carbons may be linked via a suitable element or group. In various embodiments, the term “hydrocarbyl” refers to a group having a carbon atom directly attached to the remainder of the molecule, where the group consists of carbon, hydrogen, optionally one or more heteroatoms provided the heteroatoms do not alter the predominantly hydrocarbon nature of the substituent. The heteroatom may link at least two of the carbons in the hydrocarbyl group, and optionally no more than two non-hydrocarb on substituents. Suitable heteroatoms will be apparent to those skilled in the art and include, for instance, sulphur, nitrogen, oxygen, phosphorus and silicon. Where the hydrocarbyl contains heteroatoms, optionally, no more than two heteroatoms will be present for every ten carbon atoms in the hydrocarbyl group. Suitable non-hydrocarbon substituents will also be apparent to those skilled in the art and include, for instance, halo, hydroxy, alkoxy, mercapto, alkylmercapto, nitro, nitroso, and sulphoxy.

[0023] Examples of hydrocarbyl s within the context of the present technology therefore include:(i) hydrocarbon groups selected from aliphatic (e.g. alkyl or alkenyl), alicyclic (e.g. cycloalkyl, cycloalkenyl, cycloalkadienyl), and aromatic groups;(ii) substituted hydrocarbon groups, selected from hydrocarbon groups defined in (i) substituted with no more than two non-hydrocarb on substituents and / or one or more hydrocarbon substituents, the non-hydrocarbon substituents being selected from the group consisting of halo, hydroxy, alkoxy, mercapto, alkylmercapto, nitro, nitroso, and sulphoxy;(iii) hetero-containing hydrocarbon groups, selected from hydrocarbon groups defined in (i) containing one or more heteroatom in the ring or chain, provided that the group has no more than two heteroatoms present for every ten carbon atoms in the group, the heteroatoms being selected from sulphur, nitrogen, oxygen, phosphorus and silicon. The hetero-containing hydrocarbon groups may be substituted with no more than two non-hy- drocarbon substituents and / or one or more hydrocarbon substituents.

[0024] In some embodiments, the term “hydrocarbyl” refers to a group having a carbon atom directly attached to the remainder of the molecule, where the group consists of carbon and hydrogen atoms.

[0025] Suitable polyols include, but are not limited to, trimethylolpropane, dipentaerythritol, neopentylglycol, monopentaerythritol, polypentaerythritol, or combinations thereof. In some embodiments, the POE may comprise esters and / or complex esters of aromatic polycarboxylic acids or their anhydrides. The complex ester may be composed of oligomeric units comprised of polyol (which may include, but is not limited to: trimethylolpropane, di pentaerythritol, neopentylglycol, monopentaerythritol, polypentaerythritol), and polyacid or acid anhydride (which may include, but is not limited to: succinic, glutaric, adipic, citric, trimellitic, pyromellitic), or any mixture thereof. In yet other embodiments, the at least one polyol may be trimethylolpropane, pentaerythritol, or combinations thereof.

[0026] The complex ester may be fully or partially capped with functional (mono)carboxylic acids or (mono)alkylalcohols or singly-capped glycol ethers, or any mixture thereof. As used herein, “(mono)carboxylic” or “(mono)alkylalcohol”, means the (mono) is optional, i.e. the carboxylic or alkylalcohol compounds may be mono or poly. In some embodiments of the disclosed technology, however, only monocarboxylic and / or monoalkylalcohols will be present.

[0027] Suitable lubricating oils are not overly limited. Exemplary commercially available POE lubricant oils include, but are not limited to, Icematic®, Solest® and Emkarate® refrigeration lubricants available from CPI Engineering Services, Inc. in Midland, Michigan.

[0028] In other embodiments, the lubricating composition may comprise other well- known lubricants in addition to the POEs described above. Suitable lubricants can includeGroups I-V of the American Petroleum Institute (API) Base Oil Interchangeability Guidelines, namely:Base Oil Category Sulfur (%) Saturates (%) Viscosity IndexGroup I > 0.03 and / or < 90 80 to 120Group II < 0.03 and > 90 80 to 120Group III < 0.03 and > 90 >120(Groups I, II and III are mineral oil base stocks.) Group IV All polyalphaolefins (PAOs)Group V All others not included in Groups I, II, III or IV

[0029] The lubricating oil can comprise mineral or synthetic oils e.g., polyalphaolefin oils and / or polyester oils, and mixtures thereof. In certain embodiments the oil comprises a mineral oil base stock and may be one or more of Group I, Group II, and Group III base oils or mixtures thereof. In certain embodiments the oil is not a synthetic oil. In yet other embodiments the lubricating oil comprise other common base oils, such as alkylbenzene, polyalkylene glycol, and polyvinylether.

[0030] In one embodiment, the viscosity of the polyolester prior to blending into the disclosed lubricant composition (“neat” viscosity) is 22 cSt to 180 cSt as measured by ASTM D445 at 40 °C, for example 32 cSt. The polyolester in the disclosed lubricant composition may maybe be present in at least 85wt% to 99.8wt%, based on a total weight of the lubricant composition. Alternatively, the polyolester may be present in the lubricant composition in at least 90wt%, 95wt%, or 98wt% to 99.8wt%.Dithiodialkylphosphoric Acid Ester

[0031] In some embodiments, the lubricant composition may comprise at least one dithiodialkylphosphoric acid ester that has at least one alkyl group of 3 to 8 carbon atoms. In other embodiments, the at least one dithiodialkylphosphoric acid ester may have at least two alkyl groups of 3 to 8 carbon atoms.

[0032] In some embodiments, the dithiodialkylphosphoric acid ester may be represented by the formula: s ..R’O - P - SR--OR1wherein each R1may independently be a linear or branched alkyl group containing 3 to 8 carbon atoms; and R2may be a hydrocarbyl group containing 2 to 12 carbon atoms or an acylated hydrocarbyl group containing 3 to 12 carbon atoms.

[0033] In yet other embodiments, the dithiodialkylphosphoric acid ester may be represented by the formula:OR1wherein each R1may independently be a linear or branched alkyl group containing 3 to 8 carbon atoms; and R3may be a hydrocarbyl group containing 1 to 6 carbon atoms.

[0034] In yet another embodiment, the dithiodialkylphosphoric acid ester may be methyl 3-((dialkoxyphosphorothioyl)thio)propanoate, wherein the alkoxy groups are a mixture of isobutyl and amyl (65:35 mokmol). In some embodiments, the dithiodialkylphosphoric acid ester may present in an amount to provide 600 ppm to 1200 ppm phosphorus by mass to the lubricant composition. The dithiodialkylphosphoric acid ester may be present at 0.1 to lwt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%), based on a total weight of the lubricant composition.Triazole Compound

[0035] In some embodiments, the lubricant composition may comprise at least one triazole compound that is an alkyl-substituted triazole, an aryl -substituted triazole, or mixtures thereof. Accordingly, in some embodiments, the substituted triazole includes at least one hydrocarbyl group linked to one of the nitrogen atoms in the triazole ring. In some of these embodiments the hydrocarbyl group linked to one of the nitrogen atoms in the triazole ring does not contain any oxygen atoms. The substituted triazoles include substituted benzotriazoles.

[0036] In some embodiments the substituted triazole has a single hydrocarbyl group linked to a nitrogen atom on the triazole ring. In some embodiments the substituted triazole contains an aryl group linked and a single hydrocarbyl group linked to a nitrogen atom on the triazole ring. The hydrocarbyl group may be linear or branched, however in some embodiments the hydrocarbyl group is branched. In some embodiments the hydrocarbyl contains at least one nitrogen atom, and in further embodiments the hydrocarbyl contains a single nitrogen atom. In these embodiments, where a nitrogen atom is present, the substituent group is still referred to herein as a hydrocarbyl group. In still further embodiments the hydrocarbyl group contains a single nitrogen atom, is branched at one or more points, and the nitrogen atom is itself a branch point. In other words, in some embodiments the hydrocarbyl group of the substituted triazole can be described as -R1- NR2R2where each R1is a hydrocarbyl group, and more specifically a hydrocarbylene group, and each R2is a hydrocarbyl group that contains at least one carbon atom. In such embodiments the R1and R2groups may themselves be linear or branched hydrocarbyl groups. In some embodiments R1is a linear hydrocarbyl group while both R2groups are identical branched hydrocarbyl groups.

[0037] In any of these described embodiments the hydrocarbyl group linked to one of the nitrogen atoms in the triazole ring may contain from 6 to 40 carbon atoms, or may contain from about 6, 8, 10, 12, 14, or 16 carbon atoms up to 40, 30, 20, or 18 carbon atoms. In some embodiments the hydrocarbyl group contains 16 to 18 carbon atoms and one nitrogen atom.

[0038] In some embodiments the hydrocarbyl group linked to one of the nitrogen atoms in the triazole ring is a nitrogen-containing group where the nitrogen atom in the hydrocarbyl group is connected to the nitrogen in the triazole ring by one or two carbon atoms and wherein the nitrogen atom itself also contains two hydrocarbyl groups which are identical branched alkyl groups containing 6 to 10 carbon atoms each. Examples of suitable branched alkyl groups include 2-methylpentyl, 2-methylhexyl, 3 -methylheptyl, 4-methyloctyl, 2-ethylpentyl, 2-ethylhexyl, 3 -ethylheptyl, 4-ethyloctyl, 2-propylheptyl, etc.

[0039] In some embodiments, the least one triazole compound may be a benzotriazole compound. Exemplary benzotriazole compounds include benzotriazoles represented by the formula:wherein R is hydrogen or a hydrocarbyl group of 1 to 6 carbon atoms. In yet another embodiment, the triazole compound may be methylbenzotri azole. The triazole compound may be present at 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%), based on a total weight of the lubricant composition.Phenol-Based Antioxidant

[0040] Antioxidants may be classified into compounds which prevent oxidation (complex formers, reducing agents and the like) and into compounds which interrupt the free radical chain reactions. Suitable antioxidants include phenol-based antioxidants. Exemplary phenolic antioxidants that may be used include C7-C9 branched alkyl esters of 3,5-bis(l,l-dimethyl-ethyl)-4-hydroxy-benzenepropanoic acid, 2-tert-butylphenol, 2- tert-butyl-4-methylphenol, 2-tert-butyl-5-methylphenol, 2,4-di-tert-butylphenol, 2,4-di- methyl-6-tert-butylphenol, 2-tert-butyl-4-methoxyphenol, 3-tert-butyl-4-methoxyphenol, 2,5-di-tert-butylhydroquinone, 2,6-di-tert-butyl-4-alkylphenols such as 2,6-di-tert-bu- tylphenol, 2,6-di-tert-butyl-4-methylphenol and 2,6-di-tert-butyl-4-ethylphenol, 2,6-di- tert-butyl-4-alkoxyphenols such as 2,6-di-tert-butyl-4-methoxyphenol and 2,6-di-tert- butyl-4-ethoxyphenol, 3,5-di-tert-butyl-4-hydroxybenzylmercaptooctylacetate, alkyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl)propionates such as n-octadecyl-3-(3,5-di-tert-butyl- 4-hydroxyphenyl)propi onate, n-butyl-3-(3, 5-di -tert -butyl-4-hydroxyphenyl)propi onate and 2'-ethylhexyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2,6-di-tert-butyl-a- dimethylamino-p-cresol, 2,2'-methylene-bis(4-alkyl-6-tert-butylphenol) such as 2,2'- methylenebis(4-methyl-6-tert-butylphenol, and 2,2-methylenebis(4-ethyl-6-tert-bu- tylphenol), bisphenols such as 4,4'-butylidenebis(3-methyl-6-tert-butylphenol, 4,4'- methylenebis(2,6-di-tert-butylphenol), 4, 4'-bis(2,6-di -tert -butylphenol), 2,2-(di-p-hy- droxyphenyl)propane, 2, 2-bis(3, 5 -di -tert-butyl -4-hydroxyphenyl)propane, 4,4'-cyclo- hexylidenebis(2,6-tert-butylphenol), hexamethyleneglycol -bis[3-(3, 5-di -tert-butyl-4-hy- droxyphenyl)propi onate], triethyleneglycolbis[3-(3-tert-butyl-4-hydroxy-5- methylphenyl)propi onate], 2,2'-thio-[diethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)pro- pionate], 3,9-bis{l,l-dimethyl-2-[3-(3-tert-butyl-4-hydroxy-5-methyl-phenyl)propio- nyloxy]ethyl}2,4,8,10-tetraoxaspiro[5,5]undecane, 4, 4'-thiobis(3-methyl-6-tert -butylphenol) and 2,2'-thiobis(4,6-di-tert-butylresorcinol), polyphenols such astetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane, 1,1,3- tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, l,3,5-trimethyl-2,4,6-tris(3,5-di-tert- butyl-4-hydroxybenzyl)benzene, bis-[3,3'-bis(4'-hydroxy-3'-tert-butylphenyl)butyric acid]glycol ester, 2-(3',5'-di-tert-butyl-4-hydroxyphenyl)methyl-4-(2",4"-di-tert-butyl- 3"-hydroxyphenyl)methyl-6-tert-butylphenol and 2,6-bis(2'-hydroxy-3'-tert-butyl-5'- methylbenzyl)-4-methylphenol, and p-t-butylphenol-formaldehyde condensates and p-t- butylphenol-acetaldehyde condensates.

[0041] Phenol -based antioxidants often contain a secondary butyl and / or a tertiary butyl group as a steric hindering group. The phenol group may be further substituted with a hydrocarbyl group (e.g., a linear or branched alkyl) and / or a bridging group linking to a second aromatic group.

[0042] Examples of particularly suitable hindered phenol antioxidants include 2,6- di -tert -butylphenol, 4,4'-methylenebis-(2,6-di-tert-butylphenol), 4-methyl-2,6-di-tert-bu- tylphenol, 4-ethyl-2,6-di-tert-butylphenol, 4-propyl-2,6-di-tert-butylphenol, 4-butyl-2,6- di -tert -butylphenol, 4-dodecyl-2,6-di -tert -butylphenol, 2,2'-methylenebis(4-methyl-6- tert-butylphenol), 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), as described, for example, in U.S. Pub. Nos. 2009 / 0111720, 2010 / 0269774, and 2012 / 0103290. In one embodiment, the hindered phenol antioxidant may be an ester, such as those described in U.S. Pat. No. 6,559,105, such as an alkyl alcohol esters of 3-(4-hydroxy-3,5-di -tert-butyl - phenyl)propionic acid. One such hindered phenol ester is sold as Irganox™ L-135, obtainable from BASF.

[0043] In some embodiments, the lubricant composition may comprise at least one phenol -based antioxidant comprising 2,6-di-t-butylphenol, a substituted a 2,6-di-t-bu- tylphenol, or combinations thereof. In yet other embodiments, the phenol-based antioxidant may be butylated hydroxytoluene (BHT) or butylated hydroxyanisol (BHA), or combinations thereof. The at least one phenol-based antioxidant may be present at 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%), based on a total weight of the lubricant composition.

[0044] In some embodiments, the lubricant composition may be free or substantially free of diarylamine compounds, for example N,N’-dinonylated diphenylamine. As used herein, the term “substantially free of’ means that the material in question is only present in amounts consistent with contamination and / or by-products present in commercial grades of desired components. Such materials will generally not be intentionally addedto the lubricant composition. In some embodiments, the lubricant composition comprises less than 0.1, or 0.075, or 0.05, or 0.01, or 0wt% of diarylamine compounds. Fluorinated Refrigerant

[0045] In some embodiments, the lubricant compositions may be used with fluorinated refrigerants comprising at least 30wt% or 50wt% of a polyfluorinated hydrocarbon containing 1 to 6 or 2 to 6 carbon atoms. In some embodiments, all the carbon bonds are saturated. In some embodiments the lubricant composition may be used with a fluorinated refrigerant comprising a polyfluorinated hydrocarbon that is a fluorinated olefin containing 2 to 5 carbon atoms. In the same or other embodiments, the polyfluorinated hydrocarbon of the fluorinated refrigerant may contain 2 to 6 fluorine atoms. Suitable fluorinated refrigerants include fluorinated alkanes, such as R32, R-134a, R-404A, R- 410A, or combinations thereof. In yet other embodiments, the fluorinated refrigerant may further comprise at least 10wt% of a fluorinated alkane containing 1 to 4 carbon atoms, for example polyfluorinated propylene or fluorinated methane. In yet other embodiments, the fluorinated refrigerant may further comprise at least 10wt% fluorinated methane or a fluorinated alkene containing 2 to 4 carbon atoms, for example polyfluorinated propene. In some embodiments, the refrigerant contains both fluorinated methane and a fluorinated alkene. In some embodiments, the fluorinated refrigerant may comprise at least 50wt% 2,3,3,3-tetrafluoro-propene and 10wt% to 30wt% difluoromethane. In yet other embodiments, the fluorinated refrigerant may further comprise up to 7wt% carbon dioxide. In some embodiments all of the carbon atoms in the fluorinated refrigerant are saturated.Industrial Applications

[0046] The disclosed lubricant compositions are suitable for use in heat transfer equipment and systems. Accordingly, a heat transfer system charged with the lubricant composition as described above is disclosed. Exemplary heat transfer systems include, but are not limited to, heat pump systems, refrigeration systems, and air-conditioning systems.

[0047] Methods of improving stability in a heat transfer system charged with a lubricant composition comprising at least 85wt% of a polyolester are also disclosed. The methods may comprise, adding to the lubricant composition, an additive composition comprising: 0.1 to lwt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%) of at least one dithiodialkylphosphoric acid ester; 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one triazole compound; and 0.075 to 0.3wt% (or0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one phenol-based antioxidant. The improvement in stability may be measured using the ASHRAE 97 standard test.

[0048] In other embodiments, methods of improving the extreme pressure properties of a lubricant composition comprising at least 85wt% of a polyolester are disclosed. The methods may comprise, adding to the lubricant composition an additive composition comprising: 0.1 to lwt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%) of at least one dithiodialkylphosphoric acid ester; 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one triazole compound; and 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one phenol-based antioxidant. The improvement to the extreme pressure properties of the lubricant composition may be measured using the ASTM D3233 standard test.

[0049] The uses of an additive composition to improve stability in a heat transfer system charged with a lubricant composition or improve the extreme pressure properties of lubricant composition are disclosed. The additive composition may comprise: 0.1 to 1 wt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%) of at least one dithiodialkylphosphoric acid ester; 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one triazole compound; and 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one phenol-based antioxidant. The improvement in stability may be measured using the ASHRAE 97 standard test. The improvement in extreme pressure properties may be measured using the ASTM D3233 standard test.

[0050] The amount of each chemical component described is presented exclusive of any solvent or diluent oil, which may be customarily present in the commercial material, that is, on an active chemical basis, unless otherwise indicated. However, unless otherwise indicated, each chemical or composition referred to herein should be interpreted as being a commercial grade material which may contain the isomers, by-products, derivatives, and other such materials which are normally understood to be present in the commercial grade.

[0051] It is known that some of the materials described above may interact in the final formulation, so that the components of the final formulation may be different from those that are initially added. For instance, metal ions (of, e.g., a detergent) can migrate to other acidic or anionic sites of other molecules. The products formed thereby, including the products formed upon employing the composition of the present invention in its intended use, may not be susceptible of easy description. Nevertheless, all such modifications andreaction products are included within the scope of the present invention; the present invention encompasses the composition prepared by admixing the components described above.

[0052] The lubricant composition samples herein are useful for refrigeration applica- tions, which may be better understood with reference to the following examples.EXAMPLESA - Control - polyolester with BHTB - Inventive Example C - Comparative Example1 - Methyl 3-((dialkoxyphosphorothioyl)thio)propanoate, alkoxy groups are a mixture of isobutyl and amyl (65:35 mokmol)ASHRAE 97 Tests

[0053] Each of the documents referred to above is incorporated herein by reference, including any prior applications, whether or not specifically listed above, from which priority is claimed. The mention of any document is not an admission that such document qualifies as prior art or constitutes the general knowledge of the skilled person in any jurisdiction. Except in the Examples, or where otherwise explicitly indicated, all numerical quantities in this description specifying amounts of materials, reaction conditions, molecular weights, number of carbon atoms, and the like, are to be understood as modified by the word "about." It is to be understood that the upper and lower amount, range, and ratio limits set forth herein may be independently combined. Similarly, the ranges and amounts for each element of the invention can be used together with ranges or amounts for any of the other elements.

[0054] As used herein, the transitional term “comprising,” which is synonymous with “including,” “containing,” or “characterized by,” is inclusive or open-ended and does not exclude additional, un-recited elements or method steps. However, in each recitation of “comprising” herein, it is intended that the term also encompass, as alternative embodiments, the phrases “consisting essentially of’ and “consisting of,” where “consisting of’ excludes any element or step not specified and “consisting essentially of’ permits the inclusion of additional un-recited elements or steps that do not materially affect the basic and novel characteristics of the composition or method under consideration.

[0055] While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. In this regard, the scope of the invention is to be limited only by the following claims.

Claims

What is claimed is:

1. A lubricant composition for use with a fluorinated refrigerant, wherein the lubricant composition comprises: a. at least 85wt% of a polyolester; b. 0.1 to lwt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%) of at least one dithiodialkylphosphoric acid ester; c. 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one triazole compound; and d. 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one phenol-based antioxidant; and wherein the fluorinated refrigerant comprises at least 30wt% (or at least 50wt%) of a polyfluorinated hydrocarbon containing 1 to 6 (or 2 to 6, or 2 to 5) carbon atoms.

2. The lubricant composition of claim 1, wherein the polyolester comprises an at least one polyol that is esterified with at least one linear or branched hydro- carbyl acid having 4 to 12 carbon atoms.

3. The lubricant composition of claim 2, wherein the at least one linear or branched hydrocarbyl acid is a Cs linear hydrocarbyl acid, a C7 linear hydro- carbyl acid, a C9 branched hydrocarbyl acid, or combinations thereof.

4. The lubricant composition of any preceding claim, wherein the at least one polyol is trimethylolpropane, pentaerythritol, or combinations thereof.

5. The lubricant composition of any preceding claim, wherein the at least one dithiodialkylphosphoric acid ester has at least one alkyl group of 3 to 8 carbon atoms.

6. The lubricant composition of any preceding claim, wherein the at least one dithiodialkylphosphoric acid ester has at least two alkyl groups of 3 to 8 carbon atoms.

7. The lubricant composition of any preceding claim, wherein the dithiodialkylphosphoric acid ester is represented by the formula:wherein each R1is independently a linear or branched alkyl group containing 3 to 8 carbon atoms; and R2is a hydrocarbyl group containing 2 to 12 carbon atoms or an acylated hydrocarbyl group containing 3 to 12 carbon atoms.

8. The lubricant composition of any preceding claim, wherein the dithiodial- kylphosphoric acid ester is represented by the formula:

9. wherein each R1is independently a linear or branched alkyl group containing 3 to 8 carbon atoms; and R3is a hydrocarbyl group containing 1 to 6 carbon at- oms.

10. The lubricant composition of any preceding claim, wherein the dithiodialkylphosphoric acid ester is present in an amount to provide 600 ppm to 1200 ppm phosphorus by mass to the lubricant composition.

11. The lubricant composition of any preceding claim, wherein the least one triazole compound is an alkyl-substituted triazole, an aryl -substituted triazole, or mixtures thereof.

12. The lubricant composition of any preceding claim, wherein the least one triazole compound is a benzotriazole compound.

13. The lubricant composition of any preceding claim, wherein the triazole compound is represented by the formula:wherein R is hydrogen or a hydrocarbyl group of 1 to 6 carbon atoms.

14. The lubricant composition of any preceding claim, wherein the at least one phenol-based antioxidant comprises 2,6-di-t-butylphenol, a substituted a 2,6-di-t- butylphenol, or combinations thereof.

15. The lubricant composition of any preceding claim, wherein the phenol -based antioxidant is butylated hydroxytoluene (BHT) or butylated hydroxyanisol (BHA), or combinations thereof.

16. The lubricant composition of any preceding claim, wherein the lubricant composition is free or substantially free (less than 0.1, or 0.075, or 0.05, or 0.01, or 0 wt%) of diarylamine compounds, for example N,N’-dinonylated diphenylamine.

17. The lubricant composition of any preceding claim, wherein the polyfluorinated hydrocarbon of the fluorinated refrigerant comprises a fluorinated olefin containing 2 to 5 carbon atoms.

18. The lubricant composition of any preceding claim, wherein the polyfluorinated hydrocarbon of the fluorinated refrigerant contains 2 to 6 fluorine atoms.

19. The lubricant composition of any preceding claim, wherein the fluorinated refrigerant further comprises at least 10wt% of a fluorinated alkane containing 1 to 4 carbon atoms.

20. The lubricant composition of any preceding claim, wherein the fluorinated refrigerant comprises polyfluorinated propylene and fluorinated methane.

21. The lubricant composition of any preceding claim, wherein the fluorinated refrigerant comprises at least 50wt% 2, 3, 3, 3 -tetrafluoro-propene and 10wt% to 30wt% weight percent difluoromethane.

22. The lubricant composition of any preceding claim, wherein the fluorinated refrigerant further comprises up to 7wt% carbon dioxide.1823. A heat transfer system charged with the lubricant composition of any preceding claim.

24. The heat transfer system of claim 23, wherein the heat transfer system is selected from a heat pump system, refrigeration system, and air-conditioning system.

25. A method of improving stability in a heat transfer system charged with a lubricant composition comprising at least 85wt% of a polyolester, the method comprising, adding to the lubricant composition an additive composition comprising: a. 0.1 to lwt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%) of at least one dithiodialkylphosphoric acid ester; b. 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one triazole compound; and c. 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one phenol-based antioxidant.

26. The method of claim 25, wherein the stability is improved as measured using the ASHRAE 97 standard test.

27. A method of improving the extreme pressure properties of a lubricant composition comprising at least 85wt% of a polyolester, the method comprising, adding to the lubricant composition an additive composition comprising: a. 0.1 to lwt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%) of at least one dithiodialkylphosphoric acid ester; b. 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one triazole compound; and c. 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one phenol-based antioxidant.

28. The method of claim 27, wherein the extreme pressure properties are improved as measured using the ASTM D3233 standard test.

29. The use of an additive composition to improve stability in a heat transfer system charged with a lubricant composition comprising at least 85wt% of a polyolester, wherein the additive composition comprises:19a. 0.1 to lwt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%) of at least one dithiodialkylphosphoric acid ester; b. 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one triazole compound; and c. 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one phenol-based antioxidant.

30. The use of claim 29, wherein the stability is improved as measured using the ASHRAE 97 standard test.

31. The use of an additive composition to improve the extreme pressure properties of a lubricant composition comprising at least 85wt% of a polyolester, wherein the additive composition comprises: d. 0.1 to lwt% (or 0.5 to lwt%, or 0.6 to lwt%, or 0.7 to lwt%, or 0.75 to lwt%) of at least one dithiodialkylphosphoric acid ester; e. 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one triazole compound; and f. 0.075 to 0.3wt% (or 0.08 to 0.2wt%, or 0.1 to 0.2wt%) of at least one phenol-based antioxidant.

32. The use of claim 30, wherein the extreme pressure properties are improved as measured using the ASTM D3233 standard test.20

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