Liquid Compositions Containing Organic Sulfones and Sulfoxides

This invention relates to liquid compositions comprising a major amount of a fluorine-containing hydrocarbon, and a minor amount of a lubricant. More particularly, the invention relates to liquid compositions useful as refrigeration liquids.

Chlorofluorocarbons, generally referred to in the industry as CFCs, have been widely used as propellants in aerosols, although use in aerosols has been diminishing in recent years because of demands of environmentalists for the reduction if not a complete ban on the use of CFCs because of the detrimental effect of CFCs on the atmosphere's ozone layer. CFCs also have been used because of their unique combination of properties as refrigerants, foam-blowing agents, and specialty solvents within the electronics and aerospace industries. Examples of CFCs which have been utilized for these purposes include CFC-11 which is chlorotrifluoromethane, CFC-12 which is dichlorodifluoromethane, and CFC-113 which is 1,2,2-trifluoro-1,1,2-trichloroethane.

Since 1976, when the aerosol industry began to feel the pressure to reduce if not eliminate the use of CFCs, the aerosol industry has progressively moved toward the substitution of hydrocarbon propellants for CFC propellants. The hydrocarbons, such as butane, are readily available and inexpensive, and the quality of the final product generally has been unaffected by the substitution of propellants. However, the problem of finding a safe replacement of CFC refrigerants and foam-blowing agents has been more difficult to solve. Several replacement candidates have been suggested as alternatives to the fully halogenated hydrocarbons, and these include halogenated hydrocarbons containing at least some hydrogen atoms such as HCFC-22 which is difluorochloromethane, HCFC-123 which is 1,1-dichloro-2,2,2-trifluoroethane, HFC-134a which is 1,1,1,2-tetrafluoroethane and HCFC-l4lb which is 1,1-dichloro-1-fluoroethane.

The ozone depletion potential of these proposed substitutes is significantly less than the ozone depletion potential of the previously used CFCs. The ozone depletion potential is a relative measure of the capability of the material to destroy the ozone layer in the atmosphere. It is a combination of the percentage by weight of chlorine (the atom that attacks the ozone molecule) and the lifetime in the atmosphere. HCFC-22 and HFC-l34a generally are recommended as being candidates in refrigerant applications, and HFC-l34a is particularly attractive because its ozone depletion potential has been reported as being zero.

In order for any of the replacement materials to be useful as refrigerants, the materials must be compatible with the lubricant utilized in the compressor. The presently used refrigerants such as CFC-12 are readily compatible with mineral lubricating oils which are utilized as the lubricant in air-conditioner compressors. The above-described refrigerant candidates, however, have different solubility characteristics than the refrigerants presently in use. For example, mineral lubricating oil is incompatible (i.e., insoluble) with HFC-l34a. Such incompatibility results in unacceptable compressor life in compression-type refrigeration equipment including refrigerators and air-conditioners including auto, home and industrial air-conditioners. The problem is particularly evident in automotive air-conditioning systems since the compressors are not separately lubricated, and a mixture of refrigerant and lubricant circulates throughout the entire system.

In order to perform as a satisfactory refrigeration liquid, the mixture of refrigerant and lubricant must be compatible and stable over a wide temperature range such as from about 0.degree. C. and above 80.degree. C. It is generally desirable for the lubricants to be soluble in the refrigerant at concentrations of about 5 to 15% over a temperature range of from -40.degree. C. to 80.degree. C. These temperatures generally correspond to the working temperatures of an automobile air-conditioning compressor. In addition to thermal stability, the refrigeration liquids must have acceptable viscosity characteristics which are retained even at high temperatures, and the refrigeration liquid should not have a detrimental effect on materials used as seals in the compressors.

Compositions comprising a tetrafluoroethane and polyoxyalkylene glycols are discussed in U.S. Pat. No. 4,755,316. The compositions are useful in refrigeration systems. Refrigeration oils are described in U.S. Pat. Nos. 4,248,726 and 4,267,064 which comprise mixtures of a polyglycol and 0.1 to 10% of glycidyl ether type epoxy compounds, or epoxidized fatty acid monoesters, and optionally, epoxidized vegetable oil. The lubricating oils are reported to be useful in refrigerators using a halogen-containing refrigerant such as Freons 11, 12, 13, 22, 113, 114, 500 and 502 (available from DuPont), and in particular with Freon 12 or 22.

U.S. Pat. No. 4,431,557 describes fluid compositions comprised of a fluorine-containing hydrocarbon refrigerant, a hydrocarbon oil, and an alkylene oxide additive compound which improves the thermal resistance of the oil in the presence of the refrigerant. Examples of hydrocarbon oils include mineral oil, alkyl benzene oil, dibasic acid ester oil, polyglycols, etc. The composition may contain other additives including load-carrying additives such as phosphorus acid esters, phosphoric acid esters, etc. Examples of fluorocarbon refrigerants include R-11, R-12, R-113, R-114, R-500, etc.

U.S. Pat. No. 4,428,854 describes absorption refrigerant compositions for use in refrigeration systems comprising 1,1,1,2-tetrafluoroethane and an organic solvent capable of dissolving the ethane. Among the solvents disclosed are organic amides, acetonitrile, N-methyl pyrroles, N-methyl pyrrolidine, N-methyl-2-pyrrolidone, nitromethane, various dioxane derivatives, glycol ethers, butyl formate, butyl acetate, diethyl oxalate, diethyl malonate, acetone, methyl ethyl ketone, other ketones and aldehydes, triethyl phosphoric triamide, triethylene phosphate, triethyl phosphate, etc.

Stabilized absorption compositions comprising (a) a halogenated hydrocarbon refrigerant, (b) a liquid absorbent of a polyethylene glycol methyl ether, and (c) at least one stabilizer are described in U.S. Pat. No. 4,454,052. Examples of stabilizers include phosphate esters, epoxy compounds, and organotin compounds. The polyethylene glycol methyl ether-type compounds are of the general formula

wherein n is an integer of 1 to 6, and R is H, CH.sub.3 -- or CH.sub.3 CO--. A variety of halogenated hydrocarbons are described including 1,1,-difluoromethane, 1,1,1,2-tetrafluoroethane, etc.

U.S. Pat. No. 4,559,154 relates to absorption heat pumps utilizing as working fluid, a saturated fluorohydrocarbon or fluorohydrocarbon ether having from 3 to 5 carbon atoms. Solvents reported to be useful with such fluorohydrocarbons include ethers such as tetraglyme, amides which can be lactams such as the N-alkyl pyrrolidones, sulfonamides and ureas including cyclic ureas.

A liquid composition is described which comprises

(A) a major amount of a fluorine containing hydrocarbon containing one or two carbon atoms, and

(B) a minor amount of a soluble organic lubricant free of acetylenic and aromatic unsaturation and comprising at least one sulfone or sulfoxide characterized by the formulae

wherein R.sup.1 and R.sup.2 are each independently hydrocarbyl groups, --R.sup.3 O(O)CR.sup.4, --NR.sup.4 R.sup.5 or --R.sup.3 NR.sup.4 R.sup.5 groups wherein R.sup.3 is a hydrocarbylene group, and R.sup.4 and R.sup.5 are hydrocarbyl groups, or R.sup.1 and R.sup.2 are hydrocarbylene group joined together to form a cyclic moiety including the sulfur atom, or R.sup.1 is a hydrocarbyl group and R.sup.2 is OR.sup.6 wherein R.sup.6 is a hydrocarbyl group.

The liquid compositions exhibit excellent thermal stability and are useful particularly as refrigeration liquids in refrigerators and air-conditioners including auto, home and industrial air-conditioners.

Throughout this specification and claims, all parts and percentages are by weight, temperatures are in degrees Celsius, and pressures are at or near atmospheric unless otherwise clearly indicated.

As used in this specification and in the appended claims, the terms "hydrocarbyl" and "hydrocarbylene" denote a group having a carbon atom directly attached to the polar group and having a hydrocarbon or predominantly hydrocarbon character within the context of this invention. Such groups include the following:

(1) Hydrocarbon groups; that is, aliphatic, (e.g., alkyl or alkenyl), alicyclic (e.g., cycloalkyl or cycloalkenyl), and the like, as well as cyclic groups wherein the ring is completed through another portion of the molecule (that is, any two indicated substituents may together form an alicyclic group). Such groups are known to those skilled in the art. Examples include methyl, ethyl, octyl, decyl, octadecyl, cyclohexyl, etc.

(2) Substituted hydrocarbon groups; that is, groups containing non-hydrocarbon substituents which, in the context of this invention, do not alter the predominantly hydrocarbon character of the group. Those skilled in the art will be aware of suitable substituents. Examples include halo, hydroxy, alkoxy, etc.

(3) Hetero groups; that is, groups which, while predominantly hydrocarbon in character within the context of this invention, contain atoms other than carbon in a chain or ring otherwise composed of carbon atoms. Suitable hetero atoms will be apparent to those skilled in the art and include, for example, nitrogen, oxygen and sulfur.

In general, no more than about three substituents or hetero atoms, and preferably no more than one, will be present for each 10 carbon atoms in the hydrocarbyl group.

Terms such as "alkyl", "alkylene", etc. have meanings analogous to the above with respect to hydrocarbyl and hydrocarbylene.

The term "hydrocarbon-based" also has the same meaning and can be used interchangeably with the term hydrocarbyl when referring to molecular groups having a carbon atom attached directly to the polar group.

The term "lower" as used herein in conjunction with terms such as hydrocarbyl, alkyl, alkenyl, alkoxy, and the like, is intended to describe such groups which contain a total of up to 7 carbon atoms.

(A) Fluorine-Containing Hydrocarbon

The liquid compositions of the present invention comprise a major amount of a fluorine-containing hydrocarbon. That is, the fluorine-containing hydrocarbons contain at least one C--H bond as well as C--F bonds. In addition to these two essential types of bonds, the hydrocarbon also may contain other carbon-halogen bonds such as C--Cl bonds. Because the liquid compositions of the present invention are primarily intended for use as refrigerants, the fluorine-containing hydrocarbon preferably contains one or two carbon atoms, and more preferably two carbon atoms.

As noted above, the fluorine-containing hydrocarbons useful in the liquid compositions of the present invention may contain other halogens such as chlorine. However, in one preferred embodiment, the hydrocarbon contains only carbon, hydrogen and fluorine. These compounds containing only carbon, hydrogen and fluorine are referred to herein as fluorohydrocarbons. The hydrocarbons containing chlorine as well as fluorine and hydrogen are referred to as chlorofluorohydrocarbons. The fluorine-containing hydrocarbons useful in the composition of the present invention are to be distinguished from the fully halogenated hydrocarbons which have been and are being used as propellants, refrigerants and blowing agents such as CFC-11, CFC-12 and CFC-113 which have been described in the background.

Specific examples of the fluorine-containing hydrocarbons useful in the liquid compositions of the present invention, and their reported ozone depletion potentials are shown in the following Table I.

Examples of other fluorine-containing hydrocarbons which may be useful in the liquid compositions of the present invention include trifluoromethane, 1,1,1-trifluoroethane, 1,1-difluoroethane, and 1,1,2,2-tetrafluoroethane.

In general, fluorine-containing hydrocarbons which are useful as refrigerants are fluoromethanes and fluoroethanes boiling at a relatively low temperature at atmospheric pressure, e.g., below 30.degree. C. The useful fluorocarbon refrigerants serve to transfer heat in a refrigeration system by evaporating and absorbing heat at a low temperature and pressure, e.g., at ambient temperature and atmospheric pressure, and by releasing heat on condensing at a higher temperature and pressure.

The liquid compositions of the present invention contain a major amount of the fluorine-containing hydrocarbon. More generally, the liquid compositions will comprise from about 50% to about 99% by weight of the fluorine-containing hydrocarbon. In another embodiment, the liquid compositions contain from about 70% to about 99% by weight of the fluorine-containing hydrocarbon.

(B) Soluble Organic Lubricant:

In addition to the fluorine-containing hydrocarbon, the liquid compositions of the present invention contain a minor amount of a soluble organic lubricant free of acetylenic and aromatic unsaturation and comprising at least one sulfone or sulfoxide characterized by the following formulae

wherein R.sup.1 and R.sup.2 are each independently hydrocarbyl groups, --R.sup.3 O(O)CR.sup.4, --NR.sup.4 R.sup.5 or --R.sup.3 NR.sup.4 R.sup.5 groups wherein R.sup.3 is a hydrocarbylene group, and R.sup.4 and R.sup.5 are hydrocarbyl groups, or R.sup.1 and R.sup.2 are hydrocarbylene groups joined together to form a cyclic moiety including the sulfur atom, or R.sup.1 is a hydrocarbyl group and R.sup.2 is OR.sup.6 wherein R.sup.6 is a hydrocarbyl group.

The organic lubricants characterized by Formulae I and II are free of acetylenic and aromatic unsaturation. Compounds similar to Formulae I and II which contain such unsaturation generally are insoluble in the fluorine-containing hydrocarbons and are, in particular, insoluble in 1,1,1,2-tetrafluoroethane. The soluble lubricants of this invention also are preferably free of olefinic unsaturation except that some olefinic unsaturation may be present so long as the lubricant is soluble.

The sulfones which are characterized by Formula I

are particularly useful in the liquid compositions of the present invention. The sulfones may be aliphatic sulfones or cyclic sulfones, and the cyclic sulfones may be substituted or unsubstituted, although the substituted cyclic sulfones appear to be more soluble in the fluorine-containing hydrocarbons (A) than the unsubstituted cyclic sulfones and are, therefore, preferred.

The groups R.sup.1 and R.sup.2 in Formula I may be each independently hydrocarbyl groups, and in one embodiment, the hydrocarbyl groups contain from about 1 to about 24 carbon atoms.

R.sup.1 and R.sup.2 also may be --NR.sup.4 R.sup.5 groups. Where R.sup.1 is hydrocarbyl and R.sup.2 is --NR.sup.4 R.sup.5, the lubricants are sulfonamide derivatives, and when both R.sup.1 and R.sup.2 are --NR.sup.4 R.sup.5 groups, the lubricants are bis-amide or sulfamide derivatives. Examples of such compounds include N,N'-dimethylmethanesulfonamide, N,N'-diethylsulfamide; tetraethylsulfamide; N,N'-sulfonylbis(methylamine), etc.

In Formula I, R.sup.1 and R.sup.2 also may be independently --R.sup.3 NR.sup.4 R.sup.5 groups wherein R.sup.3 is a hydrocarbylene group and R.sup.4 and R.sup.5 are hydrocarbyl groups. This embodiment may be represented by the following formula

As noted above, R.sup.3 is a hydrocarbylene group, and in particular, a hydrocarbylene group containing from 1 to about 20 carbon atoms. In another embodiment, the hydrocarbylene group R.sup.3 is a lower hydrocarbylene group. Alkyl groups R.sup.4 and R.sup.5 in Formula IA are hydrocarbyl groups which preferably contain from 1 to about 20 carbon atoms. In another embodiment, hydrocarbyl groups R.sup.4 and R.sup.5 are each independently lower alkyl groups. Thus, R.sup.3 may be ethylene, propylene, butylene, etc., and R.sup.4 and R.sup.5 may each independently be methyl, ethyl, propyl, n-hexyl, etc.

In the above Formula I, R.sup.1 and R.sup.2 also may be hydrocarbylene groups joined together to form a cyclic moiety including the sulfur atom. Preferably, the cyclic moiety is a substituted cyclic moiety, and one example of a type of substituted cyclic sulfone is illustrated by the structure ##STR1## wherein R is hydrogen, a hydrocarbyl group or a hydrocarbyloxy group. Sulfones of the following structure are particularly useful ##STR2## wherein R* is hydrogen or a hydrocarbyl group. Hydrocarbyl groups containing from 1 to about 20 carbon atoms are useful. The hydrocarbyl group R* may be straight-chain or a branched-chain. Branched-chain hydrocarbyl groups are particularly useful. In another embodiment, the hydrocarbyl group R* contains from about 8 to about 15 carbon atoms.

Examples of cyclic sulfones of the types represented by Formulae IB and IC include tetramethylene sulfone, 2-methyl tetramethylene sulfone, isodecyloxy sulfolane, octadecyloxy sulfolane, etc.

The lubricant which is included in the homogeneous liquid compositions of the present invention also may be one or more sulfoxides characterized by the formula

wherein R.sup.1 and R.sup.2 are as defined above with respect to Formula I. Specific examples of sulfoxides characterized by Formula II include dimethyl sulfoxide, tetramethylene sulfoxide, etc.

The sulfone and sulfoxide compounds useful as lubricants in the liquid compositions of the present invention are either readily available commercially or can be synthesized by techniques well known to those skilled in the art. For example, sulfonamides can be prepared by the reaction of an alkyl sulfonyl halide with an amine compound containing at least one NH group. The bis-amides can be prepared by alkylating sulfamide by the reaction of sulfonyl dichloride with amine compounds.

Substituted cyclic sulfones, i.e., substituted sulfolanes, can be prepared by reacting sulfolene with an alcohol in the presence of a basic catalyst. The aliphatic sulfones such as those represented by Formula IA above can be prepared by the reaction of a sulfonyl dialcohol with two equivalents of an amine.

Sulfones of the type represented by Formula I wherein R.sup.1 and R.sup.2 are each independently --R.sup.3 O(O)CR.sup.4 can be prepared by the reaction of a sulfonyl dialcohol such as sulfonyl diethanol with two equivalents of a carboxylic acid R.sup.4 COOH. Sulfones and sulfoxides such as represented by Formulae I and II also can be prepared by oxidation of the corresponding sulfur compounds R.sup.1 SR.sup.2 which may be readily available.

The following examples illustrate the preparation of specific sulfones which are useful in the liquid compositions of the present invention.

A mixture of 304 parts (1.5 moles) of Neodol 25, a commercially available alcohol mixture comprising C-12 to C-15 alcohols (available from Shell Chemical Company), and 3 parts of potassium hydroxide is prepared in a reaction flask, and 44 parts of 3-sulfolene are added to the mixture with stirring. After about 1 hour, the mixture is warmed to 40.degree. C. and an additional 131 parts of 3-sulfolene are added. After a delay of about 30 minutes, the reaction is exothermic, and the mixture then is maintained at 40.degree. C. for 4 hours whereupon 2.6 parts of phosphoric acid are added. The mixture is filtered through a filter aid, and the filtrate is a yellow oil.

The procedure of Example 1 is repeated except that the Neodol 25 is replaced by an equivalent amount of isodecyl alcohol.

A reaction flask is charged with 129 parts (1 mole) of dibutylamine and 77 parts (0.5 mole) of sulfonyldiethanol. The mixture is heated under reflux (about 160.degree.-210.degree. C.) until water no longer collects in a trap. The residue- is filtered through a filter aid yielding 129 parts of a light-yellow liquid which is the desired product containing 7.06% nitrogen (theory, 7.44) and 9.01% sulfur (theory, 8.51).

The sulfone and sulfoxide lubricants are soluble in the fluorine-containing hydrocarbons and, in particular, in the fluorohydrocarbons such as 1,1,1,2-tetrafluoroethane. The lubricants are soluble over a wide temperature range and, in particular, at low temperatures. The solubility of the lubricants in fluorohydrocarbons such as 1,1,1,2-tetrafluoroethane at low temperatures is determined in the following manner. The lubricant (0.5 gram) is placed in a thick-walled glass vessel equipped with a removable pressure gauge. The tetrafluoroethane (4.5 grams) is condensed into the cooled (-40.degree. C.) glass vessel, and the contents are warmed to the desired temperature and mixed to determine if the lubricant is soluble in the tetrafluoroethane. If soluble, the temperature of the mixture is reduced until a separation and/or precipitate is observed. The results of this solubility test conducted with several examples of the sulfone lubricants of the present invention are summarized in the following Table III.

The liquid compositions of the present invention comprise a major amount of a fluorine-containing hydrocarbon which is not fully halogenated and a minor amount of at least one soluble organic lubricant comprising at least one sulfone or sulfoxide of the types described above with respect to Formulae (I) and (II). By "major amount" is meant an amount greater than 50% by weight such as 50.5%, 70%, 99%, etc. The term "minor amount" includes amounts less than 50% by weight such as 1%, 5%, 20%, 30% and up to 49.9%. In one embodiment, the liquid compositions of the present invention will comprise from about 70% to about 99% of the fluorine-containing hydrocarbon and from about 1 to about 30% by weight of the lubricant. In other embodiments, the liquid compositions of the present invention may contain from about 5 to about 20% by weight of the lubricant.

The liquid compositions of the present invention are characterized as having improved thermal and chemical stability over a wide temperature range. Other additives, if soluble in the liquid, known to be useful for improving the properties of halogen-containing hydrocarbon refrigerants can be included in the liquid compositions of the present invention to improve the characteristics of the liquid as a refrigerant. However, hydrocarbon oils such as mineral oil generally are not included in and are most often excluded from the liquid compositions of the invention, particularly when the fluorine-containing hydrocarbon contains no other halogen. Polyglycols and alkyl ethers which have been suggested in the prior art as useful solvents for fluorine-containing hydrocarbons are not required in the liquid compositions of the present invention and are generally omitted from the liquid compositions.

The additives which may included in the liquid compositions of the present invention to enhance the performance of the liquids include extreme-pressure and anti-wear agents, oxidation and thermal-stability improvers, corrosion-inhibitors, viscosity-index improvers, pour point and/or floc point depressants, detergents, dispersants, anti-foaming agents, viscosity adjusters, etc. As noted above, these supplementary additives must be soluble in the liquid compositions of the invention. Included among the materials which may be used as extreme-pressure and anti-wear agents are phosphates, phosphate esters, phosphites, thiophosphates such as zinc diorganodithiophosphates, chlorinated waxes, sulfurized fats and olefins, organic lead compounds, fatty acids, molybdenum complexes, borates, halogen-substituted phosphorous compounds, sulfurized Diels Alder adducts, organic sulfides, metal salts of organic acids, etc. Stearically hindered phenols, aromatic amines, dithiophosphates, phosphites, sulfides and metal salts of dithioacids are useful examples of oxidation and thermal stability improvers. Compounds useful as corrosion-inhibitors include organic acids, organic amines, organic phosphates, organic alcohols, metal sulfonates, organic phosphites, etc. VI improvers include polyolefins such as polyesterbutene, polymethacrylate, polyalkyl styrenes, etc. Pour point and floc point depressants include polymethacrylates, ethylene-vinyl acetate copolymers, succinamic acid-olefin copolymers, ethylene-alpha olefin copolymers, etc. Detergents include sulfonates, long-chain alkyl-substituted aromatic sulfonic acids, phosphonates, phenylates, metal salts of alkyl phenols, alkyl phenolaldehyde condensation products, metal salts of substituted salicylates, etc. Silicone polymers are a well known type of anti-foam agent. Viscosity adjusters are exemplified by polyisobutylene, polymethacrylates, polyalkyl styrenes, naphthenic oils, alkyl benzene oils, polyesters, polyvinyl chloride, polyphosphates, etc.

The liquid compositions of the present invention are particularly useful as refrigerants in various refrigeration systems which are compression-type systems such as refrigerators, freezers, and air-conditioners including automotive, home and industrial air-conditioners. The following examples are illustrative of the liquid compositions of the present invention. ______________________________________ Parts by Wt. ______________________________________ Example A 1,1,1,2-tetrafluoroethane (R134a) 90 Lubricant of Ex. 2 10 Example B 1,1-dichloro-2,2,2-trifluoroethane 85 Lubricant of Ex. 1 15 Example C 1,1,1,2-tetrafluoroethane 95 Lubricant of Ex. 3 5 Example D R134a 80 Dimethyl sulfoxide 20 Example E R134a 85 Methyl sulfolane 15 ______________________________________

While the invention has been explained in relation to its preferred embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.