AU2007203564B2 - A lubricating composition containing a blend of a polyol ester and an alkylbenzene - Google Patents

Description

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION INVENTION TITLE: A LUBRICATING COMPOSITION CONTAINING A BLEND OF A POLYOL ESTER AND AN ALKYLBENZENE The following statement is a full description of this invention, including the best method of performing it known to us:- 3 1/07/07.ck16740jul25fiont, I -2- SA LUBRICATING COMPOSITION CONTAINING A BLEND OF A _POLYOL ESTER AND AN ALKYLBENZENE Field of Invention This application is a divisional of Australian Application No. 2002346463, the disclosures of which are deemed to be incorporated herein.

INO

t The present invention relates to a lubricating composition for compression refrigeration containing a blend of a polyol ester and a specific alkylbenzenes. The compositions are useful with a positive displacement compressor, such as a reciprocating rotary vane, scroll, or rotary screw air compressor.

Background of the Invention Lubricating oils have been used in the past to lubricate the bearings of positive displacement compressors, to seal the rotors, and to cool the compressed gases. Lubricating oils typically used in the industry comprise a mineral oil or synthetic oil as a base oil along with various additives for a particular purpose.

Thermal and oxidative stability and varnish and deposit control are some of the important properties desirable in a lubricant for maximizing the life of the lubricant, and hence, the life of the equipment, especially under the high temperature and pressure conditions created when operating a positive displacement compressor, such as a reciprocating rotary vane, scroll, or rotary screw compressor.

It has also been desirable in the industry to provide a lubricating composition that does not deteriorate due to exposure to moisture, exposure to high temperatures or use for an extended period of time. Hydrocarbon oils have very good resistance to reactions with moisture. Polyol esters have good high temperature resistance, but lesser stability to reactions with water.

US Patent 4,046,533 teaches branched chain alkylbenzenes can be used as lubricants for refrigerants comprising halo-substituted hydrocarbons of 1 to 3 carbon atoms and at least 40% by weight fluorine. In column 2, line 30, through column 3 line 50 it details how to identify alkylbenzenes with high amounts of branching in the alkyl group and how to identify the halo-substituted hydrocarbons. The examples of the halo-substituted hydrocarbons all contain chlorine atoms.

3 1107/07.ck 674Ojul25speci.2 -3- SUS Patent 4,302,343 describes esters of hindered polyhydric alcohols having 3 to 8 hydroxyl groups and 5 to 10 carbon atoms with one or more alkanoic acids having 4 to 18 carbon atoms. The lubricant of this patent is a blend of these esters with polyether polyols. The lubricant is used for rotary screw compressors.

US Patent 4,755,316 describes polyalkylene glycol lubricants to be used with IN a new refrigerant R-134 (tetrafluoroethane) developed to minimize concerns over ozone depletion by the halo-fluorocarbons. The patent discusses that mineral oil, a Sconventional lubricant with R-12 is not miscible with R134a and thus a search was Smade for lubricating oils meeting all of the requirements of compression refrigeration along with miscibility with R134a.

EPO 422 185B published to the Lubrizol Corporation for the use of polyol esters with hydrofluorocarbon lubricants such as R134a. The preferred polyol esters in this application were those soluble with hydrofluorocarbon lubricants over the operational range of the working fluids in a compression refrigeration system. This application outlined how to select different polyol esters to obtain miscibility with R134a and other properties.

US Patent 5,342,533 describes refrigerator oil compositions for compressors that include hydrofluorocarbons and the carboxylates of polyhydric alcohols described in US 4,302,343 and EPO 422 185B. US 5,342,533 also included a phosphate or phosphite in the lubricants and optionally included small amounts of mineral oil and/or alkylbenzene.

US Patents 6,207,071 and 6,252,300 relate to alkylbenzenes of 200 to 350 molecular weight used in compression refrigeration systems with R134a and/or R125. The application shows that lubricant compositions predominantly of alkylbenzenes cause seizure of the compressor parts after extended use if the molecular weight of 60% of the alkylbenzenes does not fall within these ranges. A phosphorus compound is optionally included in the lubricant.

Summary of the Invention The present invention relates to a lubricating fluid comprising a blend of polyol esters and alkylbenzenes having low viscosity and highly branched alkyl groups. The lubricating fluid is different than most alkylbenzene oils or blends of alkylbenzenes with other oils because it is miscible with hydrofluorocarbon 3 1/07/07,ck I6740juI25speci,3 00 o refrigerants over the operational temperature range of compression refrigeration systems for air conditioning, refrigeration, freezers etc.

In a preferred embodiment, the alkylbenzene is a narrow group of branched or linear alkyl substituted benzene having a specific range of viscosity in combination with a polyol ester having good miscibility with hydrofluorocarbon in refrigerants. The blend of polyol ester and alkylbenzene can be used with or without 0 additives including other oils of lubricating viscosity to form the lubricating composition.

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SIn embodiment A, the subject of the present application, the lubricant is miscible with a refrigerant that is substantially free of chlorine or bromine containing refrigerants.

In an alternative embodiment the subject of the parent application, the refrigerant may contain chlorine containing fluorocarbon refrigerant.

The polyol ester provides good temperature stability, lubricity, and miscibility with the hydrofluorocarbon to the blend. The alkylbenzenes provide good temperature stability, lubricity, and decrease the water attraction and water sensitivity of the blend. Additives, such as antioxidants, corrosion inhibitors, metal passivating agents and other lubricating oils, can be added to the lubricating blend.

In embodiment A, the alkylbenzene is an ISO 5 alkylbenzene predominantly with a single highly branched alkyl group of 9-15 carbon atoms per benzene ring. In a more preferred embodiment that alkyl benzene is mixed with a polyol ester from a hindered polyhydric alcohol having 2 to 6 OH groups. The blend can also be used in combination with or without additives therein.

The lubricating composition of the invention may exhibit low viscosity necessary for energy efficient operation, decreased attraction and sensitivity to moisture, and excellent long term stability of the lubricant.

Detailed Description of the Preferred Embodiments This disclosure will first describe an embodiment A where the refrigerant is substantially free of chlorine or bromine containing refrigerants. Embodiment A benefits from a low viscosity alkylbenzene and substantial amounts of polyol ester to achieve miscibility between the lubricant blend and the hydrofluorocarbon refrigerant.

09/12/08.ck 6740speci,4 0 0 o Embodiment A and Lubricating Blend in General SThe lubricating blend of this invention is selected components from the broader classes of polyol esters and alkylbenzenes. Polyol esters as a class of materials include esters from alcohols having 2 or more OH groups condensed with mono and/or polycarboxylic acids to form ester linkages in the reaction product. The

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itr viscosity and thermal stability of the class varies widely. The alkylbenzenes as a 0class of materials also varies widely including mono and polyalkyl functionalized benzenes of very low viscosity to relatively high viscosity. Alkylbenzenes include at O the lower molecular weight things such as toluene that aren't typically considered as a lubricant oils and would be a gas rather than a liquid under some of the conditions in a compression refrigeration system.

An important criteria of embodiment A is that the lubricant blend of polyol ester and alkylbenzene are miscible with the selected hydrofluorocarbon refrigerant or refrigerant blend over the operational temperatures of the compression refrigeration system. Miscibility of the lubricant with the refrigerant over operational temperatures assures that the lubricant oil that might enter into the refrigeration system out of the compressor can be carried through the evaporation orifice and heat transfer equipment back to the compressor where it functions as a lubricant and that a nonmiscible lubricant portion is not present as blockage in the system restricting refrigerant movement through the system. It also assures that minimal lubricant oil films exist on the heat transfer equipment where it might interfere with the efficiency of heat transfer by acting as a thermal insulating film.

While the necessary extent of miscibility of the lubricant blend and the refrigerant may vary depending upon application in embodiment A a desired range is about 20 0 C to about 80 0 C and more preferably -10 to about 70 0 C for concentrations of and/or 20 weight percent lubricant in the refrigerant (which can be R134a or other hydrofluorocarbons or blends of hydrofluorocarbons).

A particular benefit of the lubricant blend is that low viscosity lubricants can be formulated that tend to increase the efficiency of the refrigeration system by 09/12/08ck 16740spcci,5 Sminimizing energy losses. While polyol ester blends with alkylbenzenes can be formulated to a wide variety of viscosities, preferred viscosities for embodiment A _for the neat lubricant blend lubricant without additives, refrigerant, and other diluents) is from about ISO 5 to 70, more desirably from 5 to 68, more desirably 5 to 32, and preferably 5 to 15. An ISO viscosity is basically the numerical value of the Sviscosity in units of centistokes (cSt) of the material at 40 0

C.

The alkylbenzenes though not miscible with the hydrofluorocarbons, can become miscible with the hydrofluorocarbons when the alkylbenzenes are blended with the particular polyol esters of this disclosure. The polyol esters have good high temperature stability and long service life but do have sensitivity to moisture and hydrolysis to form the starting alcohols and carboxylic acids. The alkylbenzenes alone have a problem with miscibility with hydrofluorocarbons but decrease the water sensitivity of the blend.

The alkylbenzenes are desirably used in embodiment A in the blend in amounts from about 5 to about 45 weight percent, more desirably from about 10 to about 40, still more desirably from about 15 to about 35 and preferably from about to about 35 weight percent of the blend of alkylbenzenes and polyol esters. The polyol esters are used in complementary amounts such as from about 55 to about weight percent, desirably from about 60 to about 90, more desirably from about 65 to about 85 and preferably from about 65 to about 75 weight percent of the blend of alkylbenzenes and polyol esters. Desirably at least 80, 85, or 90 wt.% of the oils of the blend are polyol esters and alkylbenzenes described below. Other oils, components, and additives may be added to the lubricant blend to impart additional properties necessary for particular applications. Additives to alkylbenzene and to polyol ester lubricants are well known to the art.

The alkyl benzenes for embodiment A desirably have a molecular weight from about 100 to about 500 and more desirably from about 200 to about 350, and preferably from about 200 to about 300. Desirably the alkylbenzenes for embodiment A have a viscosity from about 1 to about 15 cSt at 40 0 C and more desirably from about 3 to about 10 and preferably from about 3 to about 7 cSt at 0 C. Desirably in embodiment A at least 50 mole more desirably at least and preferably at least 85 mole of the alkylbenzene is monoalkyl substituted.

31/07/07,ck16740jul25speci,6 00 7 00 O-7o Desirably in embodiment A at least 50 mole more desirably at least 75, and Spreferably at least 85 mole of the alkyl groups of said alkylbenzene have two or more methyl and/or ethyl branches extending from the alkyl backbone. In both embodiments since the alkylbenzenes are reaction products from alkylation reactions, desirably at least 50 or 60 of the alkyl benzenes, more desirably at least

INO

t 75 and preferably at least 85% have from about 5 to about 40, more desirably from Sabout 7 to about 30, and preferably from about 8 to about 16 total carbon atoms attached to the benzene.

O The polyol esters can be selected from those taught in EPO 422 185B.

Desirably the polyol esters have a number average molecular weight from about 300 to about 1000 g/mole and more desirably from about 300 to about 600. Desirably the polyol esters for embodiment A have neat viscosities (without additives or refrigerant) of from about 5 to about 70, desirably from about 5 to about 68, more desirably from about 5 to about 32 and preferably from about 5 to about 22 cSt at 40 0

C.

Generally alkyl branching in the polyol component and the carboxylic acid component of the ester promote better solubility with the R134a type of hydrofluorocarbon refrigerant but also increases viscosity. Lower molecular weight polyols and carboxylic acids tend to promote lower viscosities. Carboxylic acids with 4 or less carbon atoms tend to be disfavored for incorporation into the polyol esters. Carboxylic acids with more than 10 carbon atoms can only be tolerated in small amounts less than 10 mole based on the total carboxylic acids in the polyol ester) to maintain miscibility with the hydrofluorocarbon refrigerant at low temperatures.

The polyol esters are made by reaction polyols with carboxylic acids.

Desirably the polyols have 2 to 10 hydroxyl groups per molecule and 3 to 30 carbon atoms, optionally the polyols have one or more ether linkages therein (e.g.

dipentaerythritol). More desirably the polyols on average have 4-10 carbon atoms.

While other heteroatoms other than C, H, and O are possible they are generally disfavored in the polyol. Preferred polyols for stability and miscibility reasons are hinder polyols and condensation products (polyethers) made from hindered polyols.

The preferred number of carbon atoms from hindered polyols is from 5 to 7.

09/I2/08.ck 6740speci,7 -8- Desirably at least 50 mole and more desirably at least 80 mole of the polyol esters are derived from reacting hindered polyols having 5 to 7 carbon atoms and having 2 to 4 OH groups. Hindered polyol esters are well known to the lubrication c art. They include but are not limited to neopentyl glycol, trimethylol propane, pentaerythritol, dipentaerythritol and higher polyether oligomers of pentaerythritol.

SThey are characterized by not having hydrogen atoms attached directly to the beta carbon (the alpha carbon being attached to the oxygen of the polyol or polyol ester S(depending whether you are looking at the polyol or the polyol ester)). Instead of Shaving hydrogen atoms attached to the beta carbon, other alkyl groups or hydroxymethyl groups are attached to the beta carbon. The use of these hindered polyols in making polyol esters has resulted in improved stability of the polyol esters. Other polyols that fall within the broader definition of polyols include ethylene glycol, diethylene glycol, glycerin, polyglycerine etc.

The carboxylic acids used to make the polyol esters are desirably primarily carboxylic acids of 5-10 carbon atoms such that at least 50 and more desirably at least 80 mole of the polyol esters have residues (the portion of the carboxylic acid reactant incorporated into the polyol ester) of monocarboxylic acids having from 5 to carbon atoms. Desirably the amount of di or higher functionality polycarboxylic acids is less than 10 mole of the total carboxylic acid residues in the polyol ester.

Small amounts of carboxylic acids less than 10 mole of the carboxylic acids used to make the polyol ester) can have more than 10 carbon atoms and these acid residues can contribute specific properties to the lubricant in excess to their relative number.

The lubricating blends of the present invention can also be combined with additives or both oils and additives.

Refrigerant The refrigerant for embodiment A of this disclosure is desirably predominantly at least 80, 90 or 95 a hydrofluorocarbon or a blend of different hydrofluorocarbons that provide the desired properties for the particular application. Hydrofluorocarbons are defined as compounds having 1 to 5 carbon atoms, at least one hydrogen atom per molecule and at least one fluorine atom per molecule. Desirably for embodiment A the refrigerant is free of chlorine containing 31/07/07,ckl6740jul25speci,8 -9- Sfluorocarbons. Hydrofluorocarbons generally do not have chlorine, bromine, or other atoms contained therein except as contaminants from manufacturing processes or handling. The hydrofluorocarbons include but are not limited to R-134a, R-125, R-32, R-143a and blends of thereof. The hydrofluorocarbons of interest in this disclosure are those having suitable vapor pressures and handling characteristics for I compression refrigeration. For the purposes of this disclosure compression refrigeration will include inter alia refrigeration, air conditioning, cooling, heat pumps, etc.

O Additives As aforementioned, the lubricating blend or lubricating composition according to the present invention may also contain effective amounts of additives such as antioxidants, rust and corrosion inhibitors, metal deactivators, lubricity additives, antiwear additives, or such additives as may be required. Commercially available examples of antiwear additives are additives such as tricresyl phosphate (TCP) available at Syn-O-Add, 8484® available at Akzo-Nobel, or triphenyl phosphorothionate (TPPT) available at Ciba Geigy. In general, the finished lubricant composition will contain the additive components in minor amounts sufficient to improve the performance characteristics and properties of the oil of lubricating viscosity or basestock blend, or to both the base oil and basestock blend. Generally, additives used for their known purpose can comprise from about 10% to about 0.01% by weight of the total weight of the lubricant composition, and preferably from about to about .001% by weight based on the total weight of the lubricating composition.

Examples of useful antioxidants include phenyl naphthyl amines (alpha and/or beta), diphenyl amines, including alkylated diphenyl amines. Commercially available examples of such antioxidants are Irganox L-57® available at Ciba Geigy, and Valube 81® available at Vanderbilt Chemical. Suitable antioxidants are also exemplified by phenolic antioxidants, aromatic amine antioxidants, sulfurized phenolic antioxidants, and organic phosphites, among others. Examples of the phenolic antioxidants include 2,6-di-tert-butylphenol, liquid mixtures of tertiary butylated phenols, 2,6-di-tert-butyl-4-methylphenol, 4,4'-methylenebis(2,6-di-tertbutylphenol), 2,2'-methylenebis(4-methyl-6-tert-butyl-phenol), mixed methylene- 31/07/07,ck 16740jul25speci,9 bridged polyalkyl phenols, and 4,4'-thiobis(2-methyl-6-tert-butylphenol). N,N'-Disee-butyl-p-phenylenediamine, 4-isopropylaminodiphenyl amine, phenyl-alphanaphthyl mine, phenyl-beta-naphthyl amine, and ring-alkylated diphenylamines serve as examples of aromatic amine antioxidants. Commercially available antioxidants useful for the present invention also include Ethanox® 702 available at the Ethyl SCorporation, Irganox® L-135 and Irganox® L-118, Irganox L-06® available at Ciba O Geigy, and RC-7130® available at Rhein Chemie.

Examples of suitable rust and corrosion inhibitors are neutral metal sulfonates Ssuch as calcium sulfonate, magnesium sulfonate, sodium sulfonate, barium dinonylnaphthalene sulfonate, and calcium petroleum sulfonate. Other types of rust or corrosion inhibitors which may be used comprise monocarboxylic acids and polycarboxylic acids. Examples of suitable monocarboxylic acids are oleic acids and dodecanoic acid. Suitable polycarboxylic acids include dimer and trimer acids such as are produced from such acids as tall oil fatty acids, oleic acid, and linoleic acid.

Also useful are carboxylic acid based, metal free materials, such as hydroxy alkyl carboxylic esters. Another useful type of rust inhibitor for use in the practice of this invention is comprised of the alkenyl succinic acid and alkenyl succinic anhydride corrosion inhibitors such as, for example, tetrapropenylsuccinic acid, tetrapropenylsuccinic anhydride, tetradecenylsuccinic acid, tetradecenylsuccinic anhydride, hexadecenylsuccinic acid, hexadecenylsuccinic anhydride, and the like.

Also useful are the half esters of alkenyl succinic acids having about 8 to about 24 carbon atoms in the alkenyl group with alcohols such as the polyglycols. Other suitable rust or corrosion inhibitors include ether amines; acid phosphates; amines; polyethoxylated compounds such as ethoxylated amines, ethoxylated phenols, and ethoxylated alcohols; imidazolines; and aminosuccinic acids or derivatives thereof.

Mixtures of such rust or corrosion inhibitors can be used. U.S. Patent No. 5,773,393 is incorporated in its entirety herein for its disclosure regarding rust and corrosion inhibitor additives. A commercially available example of a corrosion inhibitor is L- 859® available at the Lubrizol Corporation.

Examples of suitable metal deactivators are complex organic nitrogen, oxygen and sulfur-containing compounds. For copper, compounds such as substituted benzotriazole, alkyl or acyl substituted 31/07/07.ckl6740jul25speci. -11- (alkyl or acyl substituted 2,5-dimercaptothiazole, salts of salicylaminoguanidine, and quinizarin are useful. Propylgallate is an example of a metal deactivator for magnesium, and sebacic acid is an example of a deactivator for lead. A commercially available example of a triazole metal deactivator is Irgamet 39® available at Ciba Geigy.

An effective amount of the foregoing additives is generally in the range from about 0.005% to about 5% by weight of the total weight of the lubricant composition for the antioxidants, from about 0.005% to about 0.5% percent by weight based on the total weight of the lubricant composition for the corrosion inhibitors, and from about 0.001% to about 0.5% percent by weight of the total weight of the lubricant composition for the metal deactivators. It is to be understood that more or less of the additives may be used depending upon the circumstances for which the lubricant compositions are to be used.

The present invention also is directed to a process of lubricating a piece of equipment, for example, a positive displacement compressor such as a reciprocating rotary vane, a scroll, or a rotary screw air compressor, whereby the life of the lubricant and the equipment is maximized since the lubricant has excellent oxidative and thermal stability, The air conditioning and refrigeration systems have various operating temperature requirements for refrigeration lubricants. Generally, air conditioners need a lubricant that is miscible with the refrigerant at about 0°C to about 70 or while refrigeration systems require miscibility down below 0 C to -10 or so that freezing temperatures are maintained inside the freezer compartments).

In HFC (hydrofluorocarbon, generally chlorine and bromine free) systems, these miscibility requirements can be achieved by using PAG- (polyalkylene glycols) and POE-based (polyol ester) lubricants. However, the miscibility requirements are not achievable with the AB (alkylbenzenes) as demonstrated by the data in Table 1. It is conceivable for AB with viscosity lower than ISO 7 to have limited miscibility with HFCs. However, they (AB lubricants with ISO 7 viscosity) are not applicable in refrigeration or air-conditioning compressors due to inadequate lubrication film strength.

31/07/07.ck 16740jul25spcci, II 12- Table 1. The Miscibility of AB with R-134a AB AB-7 AB-10 AB-22 AB-32 Ester No No No No Vis 7 10 22 32 R-134a, X X X X R-134a, X X X X

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In Cc, 5% lubricant in the R-134a/lubricant solution.

X: not miscible at any temperature from -60 to 60 0

C.

AB-7: an ISO 7 AB from Shrieve Chemical an ISO 10 AB from Shrieve Chemical AB-22: an ISO 22 AB from Shrieve Chemical AB-32: an ISO 32 AB from Shrieve Chemical The miscibility of POE/AB blends is shown in Table 2. The POE/AB ratios in these blends are designed in such a way that blends can have viscosity ranged from ISO 10 to ISO 32. The POE chosen are those with high miscibility with HFCs as this is critical for improving miscibility of the blends.

The B1-B4 examples are blends made to meet the ISO 10 specification. The B3 and B4 examples show considerably better miscibility compared to BI and B2 at and 10% lubricant concentration in the refrigerant/lubricant solution and meet the requirement of refrigeration lubricants. The better miscibility is attributed to both the low viscosity AB and high miscibility POE chosen for the blends. The miscibility of lubricants with HFCs is expected to decline at higher viscosity. This makes formulating a higher viscosity POE/AB blend with adequate miscibility with HFCs difficult. The B5-B8 examples in Table 2 have viscosity ranged from 22 to 32, the data show B8 is the only blend with adequate viscosity acceptable to be used in airconditioning or refrigeration systems. Similar to the ISO 10 situation, the good miscibility of the B8 is attributed to the low viscosity AB and high miscibility of the POE 4 with HFC refrigerant.

31/07/07,ck16740ju25speci. 12 00 00 -13-

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dU Table 2. POE/AB blends Miscibility with R-134a __(Lower miscibility temperature in 0

C)

_Bl B2 B3 B4 B5 B6 B7 B8 AB 70% 30% 30% 30% 50% 30% 70% S__AB-7 AB-22 AB-5 AB-5 AB-10 AB-7 AB-22 N Ester 30% 70% 50% 30% 50% 75% 30% m POEl POE 2 POE3 POE POE1 POE4 POE4 POE4 POE2 POE2 O Vis 10 10 10 10 22 32 32 32 0 C),cSt R-134a,5%, 5 40 -30 -25 -20 -10 X R-134a, 10% 25 55 -25 -20 20 15 X POE 1: nC5, nC7, iC9, PE (pentaerythritol) POE 2: 2EH, NPG (neopentyl glycol) POE3: nC5, PE, POE4: nC5, iC8, I C9, PE Although the invention has been shown and described with respect to certain preferred embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and the understanding of the specification. The present invention includes all such equivalent alterations and modifications, and is limited only by the scope of the claims.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form or suggestion that the prior art forms part of the common general knowledge in Australia.

09/12/08,ck 16740spci, 13

Claims (10)

1. A working fluid in a compression refrigeration system comprising; a) a Shydrofluorocarbon refrigerant, b) a lubricant comprising from 15 to 45 wt.% of an alkylbenzene having a molecular weight from 100 to 500 and from 55 to 85 wt.% of a polyol ester having a molecular weight from 300 to 1000 and further wherein said t lubricant has a neat viscosity between ISO 5 and ISO 35 and at least 50 mole of Ssaid polyol ester contains a polyol residue from a hindered polyol having 2, 3, or 4 hydroxyl groups and 5 to 7 carbon atoms and at least 50 mole of the polyol ester contains at least one residue per polyol ester from a C5 monocarboxylic acid.

2. A working fluid according to claim 1, wherein said alkylbenzene has a number average molecular weight from about 200 to about 350 is at least 60 mole monoalkylated.

3. A working fluid according to claim 2, wherein at least 60 mole of the alkyl groups of said alkylbenzene are branched C8-C16 alkyls.

4. A working fluid according to claim 3, wherein at least 80 weight of said polyol ester is derived from the esterification of a hindered polyhydric alcohol with carboxylic acids having from 5 to 10 carbon atoms.

A working fluid according to claim 4, wherein said polyol ester has sufficient methyl or ethyl branching in the acid residue, or sufficient portions ofC5 or C6 acids in the acid residue of the polyol ester to not show phase separation with lubricant in R134a solution at 0°C.

6. A working fluid according to claim 4, wherein said alkylbenzene is from about 25 to 35 weight and said polyol ester is from about 65 to about 75 weight of said lubricant. 03/12/08.ck 16740claims.14 00 O O c

7. A working fluid according to claim 8, wherein said alkylbenzene has an ISO viscosity between about 3 and 7.

8. A working fluid according to claim 4, wherein said lubricant has a neat viscosity between ISO 5 and ISO CA

9. A working fluid according to claim 1 substantially as hereinbefore described O CN with reference to the Examples. N 10

10. A working fluid in a compression refrigeration system comprising; a) a hydrofluorocarbon refrigerant, b) a lubricant comprising from 15 to about 45 wt.% of an alkylbenzene having a molecular weight from about 100 to about 500 and from about 55 to about 85 wt.% of a polyol ester having a molecular weight from about 300 to 1000 and further wherein said lubricant has a neat viscosity between ISO and ISO 35 and at least 50 mole of said polyol ester contains a polyol residue from a hindered polyol having 2, 3, or 4 hydroxyl groups and 5 to 7 carbon atoms and at least 50 mole of the polyol ester contains at least one residue per polyol ester from a C5 monocarboxylic acid. 03/12/08.ck 6740claims.15