FIELD OF THE INVENTION

The present invention relates to stabilized polyoxyalkylene glycols. More particularly, the present invention relates to relates to stabilized refrigeration compositions comprising tetrafluoroethane and polyoxyalkylene glycols. Preferably, the tetrafluoroethane is 1,1,1,2-tetrafluoroethane (known in the art as R134a) . R134a is a refrigerant which may replace dichlorodifluoromethane (known in the art as R12) in many applications because environmental concerns over the use of R12 exist.

BACKGROUND OF THE INVENTION

Currently, R12 is used in closed loop refrigeration systems; many of these systems are automotive air-conditioning systems. R12 refrigeration systems generally use mineral oils to lubricate the compressor. Mineral oil is typically paraffin oil or naphthenic oil.

R134a has been mentioned as a possible replacement for R12 because concern over potential depletion of the ozone layer exists. R134a has properties similar to those of R12 so that it is possible to substitute R134a for R12 with minimal changes in equipment being required. The symmetrical isomer of R134a is R134 (1,1,2,2-tetrafluoroethane) ; the isomer is also similar in properties and may also be used. Consequently, it should be understood that in

the following discussion, "tetrafluoroethane" will refer to both R134 and R134a.

A unique problem arises in such a substitution. As mentioned earlier, refrigeration systems which use R12 generally use mineral oils to lubricate the compressor; the present discussion does not apply to absorption refrigeration equipment. See for example the discussion in Chapter 32 of the 1980 ASHRAE Systems Handbook. R12 is completely miscible with such oils throughout the entire range of refrigeration system temperatures which may range from about -45.6° to 65.6°C. Consequently, oil which dissolves in the refrigerant travels around the refrigerant loop and generally returns with the refrigerant to the compressor. The oil does not separate during condensation, although it may accumulate because low temperatures exist when the refrigerant is evaporated. At the same time, the oil which lubricates the compressor contains some refrigerant which may affect its lubricating property.

It is known in the industry that chlorodifluorome hane (known in the art as R22) and chlorodifluoromethane/1-chloro-1,1,2,2,2- pentafluoroethane (known in the art as R502) are not completely miscible in common refrigeration oils. See Downing, FLUOROCARBONS REFRIGERANT HANDBOOK, Page 13. A solution to this problem has been the use of alkylated benzene oils. Such oils are immiscible in R134a and are not useful therewith. This problem is most severe at low temperatures when a separated oil layer would have a very high viscosity. Problems of oil returning to the compressor would be severe.

R134a is not miscible with mineral oils; consequently, different lubricants will be required for use with R134a. However, as mentioned above, no major changes to equipment should be necessary when the refrigerant substitution is made. If the lubricant separates from the refrigerant, it is expected that serious operating problems could result. For example, the compressor could be inadequately lubricated if refrigerant replaces the lubricant. Significant problems in other equipment also could result if a lubricant phase separates from the refrigerant during condensation, expansion, or evaporation. These problems are expected to be most serious in automotive air-conditioning systems because the compressors are not separately lubricated and a mixture of refrigerant and lubricant circulates throughout the entire system.

Small amounts of lubricants may be soluble in R134a over a wide range of temperatures, but as the concentration of the lubricant increases, the temperature range over which complete miscibility occurs, i.e., only one liquid phase is present, narrows substantially. For any composition, two consolute temperatures, i.e., a lower and a higher temperature, may exist. That is, a relatively low temperature below which two distinct liquid phases are present and above which the two phases become miscible and a higher temperature at which the single phase disappears and two phases appear again may exist. A diagram of such a system for R502 refrigerant is shown as Figure 2 in the Kruse et al. paper mentioned above. A range of temperatures where one phase is present exists and while it would be desirable that a refrigeration system operate within such a range, it has been found that for typical compositions, the miscible range of lubricants

with R134a is not wide enough to encompass the typical refrigeration temperatures.

In response to the foregoing need in the art, polyoxyalkylene glycol lubricants which are miscible with R134a have been developed. See commonly assigned U.S. Patents 4,755,316; 4,900,463; and 4,975,212.

A problem with the polyoxyalkylene glycols facing the art is described by K.S. Sanvordenker, "Durability of R134a Compressors: The Role of the Lubricant", ASHRAE Journal, 42 (February 1991) . At temperatures above 200°C, the polyoxyalkylene glycols decompose to form water and other products. While this temperature is in the upper range of operation of most systems, it indicates that the problem could exist at lower temperatures and cause problems in systems which are subjected to severe service. This is undesirable in refrigeration and air-conditioning systems because the presence of water creates at least three problems.

First, water causes ^' corrosion of metallic parts in the system. Second, all refrigeration and air-conditioning systems have expansion valves. As refrigerant expands across an expansion valve, the refrigerant cools rapidly and water present freezes out and blocks the expansion valve. Third, some refrigeration and air- conditioning systems are hermetic. Hermetic systems use polyester or more particularly, poly(ethylene terephthalate) , films as electrical insulation for parts of the electric motor. Water reacts with pol (ethylene terephthalate) so that eventually the film is destroyed and the water contacts the electric motor parts.

If an additive substantially minimized the decomposition of polyoxyalkylene glycols, polyxoxyalkylene glycols could be used in applications wherein high temperature excursions occur without decomposition and the foregoing problems. As such, the need exists in the art for an additive which prevents the decomposition of polyoxyalkylene glycols.

Kokai Patent Publication 179,699 published October 12, 1984; and Kokai Patent Publication 281,199 published December 11, 1988 teach additives such as epoxides for refrigeration lubricants.

Commonly assigned U.S. Patent 4,755,316; Kokai Patent Publication 281,199 published December 11, 1988; U.S. Patents 4,812,246 and 4,851,144; commonly assigned U.S. Patent 4,900,463; Kokai Patent Publication 102,296 published April 13, 1990; U.S. Patent 4,959,169; and commonly assigned U.S. Patent 4,975,212 teach additives such as phenols for refrigeration lubricants.

U.S. Patents 4,248,726; 4,267,064; and 4,431,557 teach the addition of epoxides to compositions of refrigerants and lubricants. The references also teach that known additives such as phenol or amine type antioxidants; sulphur or phosphorus type oiliness improvers; silicone type antifoam agents; metal deactivators such as benzotriazole, amines, and acid esters; and load carrying additives such as phosphoric acid esters, phosphorous acid esters, thiophosphoric acid esters, organic sulfur compounds, and organic halogen compounds can be used. These references do not teach or suggest the present invention.

U.S. Patent 4,948,525 teaches that known refrigerator oil additives such as phenol-type antioxidants such as di-tert-butyl-p-cresol; amine-type antioxidants such as phenyl-α-naphthylamine and N,N'- di(2-naphthyl) -p-phenylenediamine; load resistant additives such as zinc dithiophosphate, chlorinated paraffin, fatty acids, and sulfur type load resistant compounds; silicone-type antifoaming agents; metal inactivators such as benzotriazole; and hydrogen chloride captors such as glycidyl ethacrylate and phosphite esters may be used in refrigeration compositions. The reference states that these additives may be used singly or jointly but does not teach or suggest the present invention.

SUMMARY OF THE INVENTION

In response to the need in the art, the present invention provides stabilized polyoxyalkylene glycols. We believe that the stabilized polyoxyalkylene glycols can be used in compression refrigeration and air- conditioning systems and substantially no decomposition of the polyoxyalkyene glycols occurs. The stabilized polyoxyalkylene glycols comprises: (a) polyoxyalkylene glycol and (b) a composition comprising: (i) at least one component selected from the group consisting of phenol and trivalent phosphorus compound and (ii) at least one epoxide selected from the group consisting of aromatic epoxide and fluorinated alkyl epoxide wherein the composition (b) substantially reduces the decomposition of the polyoxyalkylene glycol (a) .

In a preferred embodiment, the present invention provides a stabilized refrigeration composition

comprising: (a) a fluorine-containing refrigerant selected from the group consisting of fluorocarbon refrigerant and hydrofluorocarbon refrigerant; (b) polyoxyalkylene glycol; and (c) a composition comprising: (i) at least one component selected from the group consisting of phenol and trivalent phosphorus compound and (ii) at least one epoxide selected from the group consisting of aromatic epoxide and fluorinated alkyl epoxide wherein the composition (c) substantially reduces the decomposition of the polyoxyalkylene glycols (b) .

The term "fluorocarbon" as used herein means a compound having fluorine and carbon atoms. The term "hydrofluorocarbon" as used herein means a compound having hydrogen, fluorine, and carbon atoms.

The present invention also provides a method of substantially reducing the decomposition of polyoxyalkylene glycol. The method comprises the step of: employing a composition comprising: (i) at least one component selected from the group consisting of phenol and trivalent phosphorus compound and (ii) at least one epoxide selected from the group consisting of aromatic epoxide and fluorinated alkyl epoxide wherein the composition substantially reduces the decomposition of polyoxyalkylene glycol.

Other advantages of the present invention will become apparent from the following description and the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The stabilized polyoxyalkylene glycols of the present invention comprises: (a) polyoxyalkylene glycol and (b) a composition comprising: (i) at least one component selected from the group consisting of phenol and trivalent phosphorus compound and (ii) at least one epoxide selected from the group consisting of aromatic epoxide and fluorinated alkyl epoxide. The present stabilized polyoxyalkylene glycols are useful in compression refrigeration and air-conditioning systems.

Any combination of at least phenol and/or at least one trivalent phosphorus compound and at least one aromatic epoxide and/or at least one fluorinated alkyl epoxide which substantially reduces the decomposition of polyoxyalkylene glycols can be used in the present invention.

Preferably, the phenol is phenol selected from the group consisting of:

4,4 -methylenebis (2, 6-di-tert-butylphenol) ; 4,4 -bis(2,6-di-tert-butylphenol) ; 4,4 -bis (2-methyl-6-tert-butylphenol) ; 2,2 -methylenebis (4-ethyl-6-tert-butylphenol) ; 2,2 -methylenebis (4-methyl-6-tert-butylphenol) ; 4,4 -butylidenebis (3-methyl-6-tert-butylphenol) ; 4,4 -isopropylidenebis (2, 6-di-tert-butylphenol) ; 2,2 -methylenebis (4-methyl-6-nonylphenol) ; 2,2 -isobutylidenebis (4, 6-dimethylphenol) ; 2,2 -methylenebis (4-methyl-6-cyclohexylphenol) ; 2, 6-di-tert-butyl-4-methylphenol; 2,6-di-1ert-butyl-4-ethylphenol; 2,4-dimethyl-6-tert-butylphenol;

2,6-di-tert-butyl -a-dimethylamino-p-cresol; 2,6-di-tert-butyl-4(N,N' -dimethylaminomethylphenol) ; 4,4' -thiobis (2-methyl-6-tert-butylphenol) 4,4' -thiobis(3-methyl-6-tert-butylphenol) 2,2 ' -thiobis(4-methyl-6-tert-butylphenol) bis (3-methyl-4-hydroxy-5-tert-butylbenzyl) sulfide; bis (3,5-di-tert-butyl-4-hydroxybenzyl)sulfide; 2,2- or 4,4-biphenyldiols and derivatives thereof; hydroquinone; t-butyl hydroquinone; and other derivatives of hydroquinone.

The most preferred phenols are hydroquinone and 2,6-di-tert-4-methylphenol. The foregoing phenols are commercially available. As mentioned earlier, mixtures of phenols may be used in addition to the use of a single phenol in the present invention.

The term "phenol" as used herein includes sterically hindered phenols.

Preferably, the trivalent phosphorus compound is trivalent phosphorus compound selected from the group consisting of tris(4-nonylphenyl)phosphite; tris(2,4-di-tert-butylphenyl)phosphite; 3,9-dioctadecyloxy-2,4,8,10-tetraoxa-3,9-diphospha-

[5,5] -spiroundecane;

3,9-bis(2,4-di-tert-butylphenyloxy) -2,4,8,10-tetraoxa-

3,9-diphospha- [5,5] -spiroundecane; and tetrakis(2,4-di-tert-butylphenyl) -4,4' - biphenylenediphosphonite and mixture thereof.

The preferred trivalent phosphorus compound is tris(2,4-di-tert-butylphenyl)phosphite. The foregoing phosphorus compounds are commercially available. As mentioned earlier, mixtures of

phosphorus compounds may be used in addition to the use of a single phosphorus in the present invention.

Preferred aromatic epoxides are of the formula [Ri] _n - - tiy _a wherein R ₂ is OCH ₂ CHCH ₂ -0; R _t is hydrogen, alkyl having 1 to 20 carbon atoms, fluoroalkyl having 1 to 20 carbon atoms, aryl having 6 to 28 carbon atoms, or fluoroaryl having 1 to 28 carbon atoms; M is aryl selected from the group consisting of phenyl, naphthyl, anthracyl, and phenanthrenyl, or alkylaryl; and each n and m is from 1 to 10. More preferably, the aromatic epoxide is aromatic epoxide selected from the group consisting of butylphenylglycidyl ether; pentylphenylglycidyl ether; hexylphenylglycidyl ether; heptylphenylglycidyl ether; octylphenylglycidyl ether; nonylphenylglycidyl ether; glycidyl methyl phenyl ether; decylphenylglycidyl ether; 1,4-diglycidyl phenyl ether and derivatives thereof; 1,4-diglycidyl naphthyl ether and derivatives thereof; 2,2' [[[5- heptadecafluorooctyl] 1,3phenylene]bis [[2,2,2trifluorome thyl]ethylidene]oxymethylene]bisoxirane and derivatives thereof; naphthyl glycidyl ether; 4-methoxyphenyl glycidyl ether; and derivatives of naphthyl glycidyl ether.

The most preferred aromatic epoxide is naphthyl glycidyl ether. Some of the foregoing aromatic epoxides are commercially available. As mentioned earlier, mixtures of aromatic epoxides may be used in addition to the use of a single aromatic epoxide in the present invention.

Preferred fluorinated alkyl epoxides are of the formula

wherein R _f is fluor nated or perfluorinated alkyl group having 1 to 20 carbon atoms. More preferably, the fluorinated alkyl epoxide is fluorinated alkyl epoxide selected from the group consisting of glycidyl trifluoromethyl ether; glycidyl pentafluoroethyl ether; glycidyl heptafluoropropyl ether; and glycidyl monofluorobutyl ether.

The most preferred fluorinated alkyl epoxide is glycidyl pentafluoroethyl ether. The foregoing fluorinated alkyl epoxides are commercially available. As mentioned earlier, mixtures of fluorinated alkyl epoxides may be used in addition to the use of a single fluorinated alkyl epoxide.

The ratio of phenol or phosphorus to epoxide in the stabilizing polyoxyalkylene glycols can be varied from 1:99 to 99:1. Preferably, the amount of phenol and aromatic or fluorinated alkyl epoxide used is about 0.01 to about 5 percent by weight based on the amount of the polyoxyalkylene glycols.

Any polyoxyalkylene glycol can be used in the present invention. Preferred polyoxyalkylene glycols include the polyoxyalkylene glycols of commonly assigned U.S. Patent 4,755,316 which is incorporated herein by reference. Such polyoxyalkylene glycols have a molecular weight between about 300 and about 2000, a viscosity of about 25 to about 150 centistokes at 37°C, and a viscosity index of at least 20. The polyoxyalkylene glycols preferably have at least 80 percent propylene oxide units; the remaining units may be ethylene oxide, butylene oxide, or other units such as esters and olefins which may be polymerized with

propylene oxide.

The polyoxyalkylene glycols may also be capped with at least one hydrocarbon group such as alkyl, aryl, or ester. A preferred example of such a capped polyoxyalkylene glycol is a copolymer of ethylene oxide and propylene oxide wherein one end is capped with a butyl group.

Other preferred polyoxyalkylene glycols include the polyoxyalkylene glycols having a cap of a fluorinated alkyl group on at least one end thereof of commonly assigned U.S. Patent 4,975,212 which is incorporated herein by reference. These glycols have a molecular weight between about 300 and about 3,000, a viscosity of about 5 to about 150 centistokes at 37°C, and a viscosity index of at least 20.

Preferably, the foregoing fluorinated lubricants comprise the formula (I)

R ₁ OR ₂ [AO] _m (BO) _n R ₄ wherein m is 4 to 36, n is 0 to 36, R ₂ is -CH(CH ₃ )CH ₂ - or a direct bond, R. and R ₄ are independently selected from the group consisting of hydrogen, alkyl group, and fluorinated alkyl group, Rj can also be a residue of a compound having 1 to 8 active hydrogens, and A and B are the same or different and selected from the group consisting of methyl, ethyl, propyl, or butyl. At least one of R, and R ₄ is a fluorinated alkyl group. Examples of alkyl groups include methyl, ethyl, propyl, and butyl. The lubricant may be terminated by a hydrogen at one end and a fluorinated alkyl group at the other end, by an alkyl group at one end and a fluorinated alkyl group at the other end, or by a fluorinated alkyl group at both ends. The fluorinated

alkyl group may be branched or straight chain as long as fluorine atoms are attached thereto.

The foregoing fluorinated lubricants may be formed by fluorinating polyoxyalkylene glycols. The polyoxyalkylene glycols used may have primary carbons at both ends, a primary carbon at one end and a secondary carbon at the other end, or secondary carbons at both ends. Preferably, the polyoxyalkylene glycols used have a primary carbon at one end and a secondary carbon at the other end or secondary carbons at both ends.

In a more preferred embodiment, at least one of R, and R is a fluorinated alkyl group of the formula

(II) :

-(CH ₂ ) _x (CF ₂ ) _y CF ₃ wherein x is 1 to 4 and y is 0 to 15. More preferably, x is 1 and y is 0 so that at least one of R. and R ₄ is a fluorinated alkyl group of the formula -CH ₂ CF ₃ or x is 1 and y is 2 so that at least one of R _! and R ₄ is a fluorinated alkyl group of the formula -CH ₂ (CF ₂ ) ₂ CF ₃ . Even more preferably, both R, and R, are fluorinated alkyl groups, m is 7 to 34, and n is 0.

The most preferred lubricating compositions are

CF ₃ CH ₂ 0 [CH _j CH (CH ₃ 0) ] _m CH ₂ CF ₃ CF ₃ (CF ₂ ) ₂ CH ₂ 0 [CH ₂ CH (CH ₃ ) 0] _m CH ₂ (CF ₂ ) ₂ CF ₃

CF ₃ (CF ₂ ) ₂ CH ₂ 0CH (CH ₃ ) CH ₂ 0 [CH ₂ CH (CH ₃ ) 0] _m CH ₂ (CF ₂ ) ₂ CF ₃ where m is 7 to 34 .

Generally, the foregoing fluorinated lubricating compositions may be formed by capping a polyoxyalkylene

glycol with at least one fluorinated alkyl group. The lubricating compositions may be formed by copoly erizing ethylene and propylene oxides and terminating the resulting copolymer with at least one fluorinated alkyl group.

Preferably, the foregoing fluorinated lubricants wherein one end has an alkyl group and the other end has a fluorinated alkyl group or both ends have fluorinated alkyl groups are formed as follows. The polyoxyalkylene glycol is converted to the tosylate by treatment with p-toluenesulfonyl chloride in a suitable base such as pyridine and then the tosylated polyglycol is reacted with the sodium alkoxide of the appropriate fluorinated alcohol.

Preferably, the foregoing fluorinated lubricants wherein one end has a h droxyl group and the other has a fluorinated alkyl group are formed as follows. An alcohol initiator such as the sodium alkoxide of trifluoroethanol is used in the polymerization of polypropylene oxide.

Most preferably, the fluorinated lubricant is a fluorinated copolymer of butylene oxide and propylene oxide or is a mixture of fluorinated butylene oxide and fluorinated propylene oxide.

In a preferred embodiment, the stabilized polyoxyalkylene glycols are used with a fluorine- containing refrigerant to form a refrigeration composition. The present refrigeration compositions are useful in compression refrigeration and air- conditioning systems. Preferably, the fluorocarbon or hydrofluorocarbon refrigerant is selected from those

listed those listed in Table I below.

The above fluorocarbon and hydrofluorocarbon refrigerants are commercially available. Preferably, R134a is used. Until R134a becomes available in commercial quantities, it may be produced by any known method including reacting ethylene with carbon having elemental fluorine adsorbed therein as taught by commonly assigned U.S. Patent 4,937,398 which is incorporated herein by reference.

Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.