REFRIGERATION WORKING FLUID COMPOSITIONS FOR USE IN RECOMPRESSION TYPE COOLING SYSTEMS

Abstract: A refrigeration working fluid composition which is miscible or partially miscible at temperatures of less than 120 DEG C and which is immiscible at temperatures of at least about 120-180 DEG C, the refrigeration working fluid comprising: (i) about 65 to 95 weight % of a refrigerant, based on the total weight of the working fluid composition, the refrigerant comprising a blend of pentafluoroethane, 1,1,1-trifluoroethane, and 1,1,1,2-tetrafluorothane, wherein the tetrafluoroethane is present in an amount of between about 0.5 to 10 weight %, based on the total weight of the refrigerant, and (ii) about 5 to 35 weight % of a polyol ester lubricant, based on the total weight of the working fluid composition.

Description: REFRIGERATION WORKING FLUID COMPOSITIONS FOR USE IN RECOMPRESSION TYPE COOLING SYSTEMS This is a continuation-in-part of U.S. Patent Application, Serial No. 08/340,961. The invention relates to refrigeration working fluid compositions uniquely designed for efficient operation in recompression type cooling system. More particularly this invention relates to refrigeration working fluid compositions comprising fluorocarbon (HFC) refrigerant blends and certain polyol ester lubricants having suitable viscosities and which are miscible with the refrigerant at low temperatures (i.e., below 120°C) while immiscible at higher temperatures (i.e., about 120-180°C or greater), thereby exhibiting reversible miscibility. BACKGROUND OF THE INVENTION Cooling systems of the mechanical vapor recompression type, including refrigerators, freezers, heat pumps, air conditioning systems, and the like, are well known. In such devices, a refrigerant of suitable boiling point evaporates at low pressure, taking heat from the surrounding zone. The resulting vapor is then compressed and passed to a condenser where it condenses and gives off heat to a second zone. The condensate is then returned through an expansion valve to the evaporator, so completing the cycle. It is recognized that currently used refrigerants which contain chlorine, such as dichlorodifluoromethane, will be replaced by chlorine- free refrigerant fluids because of the adverse effect of the chlorinated materials upon the atmospheric ozone layer. Tetrafiuoroethane isomers and in particular "Refrigerant 134a", which is 1, 1, 1, 2-tetrafluoroethane, are now considered desirable fluids for use in refrigeration systems. Re rigeration working fluids are required to have a lubricant which is compatible and miscible with the refrigerant so that moving parts of the system are properly lubricated. Heretofore, such lubricants have been composed of hydrocarbon mineral oils which are miscible with the chlorine-containing refrigerant fluids and which provide effective lubrication. The use of chlorine-free, HFC (hydrofluorocarbon) refrigerants has created a need for new lubricants, since mineral oils are not compatible with these materials. This need is well recognized in the art and there are numerous recent publications and patents disclosing various types of synthetic lubricants which are said to be compatible with tetrafiuoroethane refrigerant fluids. Esters of polyols are being particularly emphasized as being suitable for use with the tetrafiuoroethane refrigerants, especially refrigerant R134a. U.S. Patent 5,021,179, issued June 4, 1991 to Zehler et al. , discloses esters of polyols in which the acyl groups have at least 22% of (a) branched acyl groups or (b) acyl groups which contain no more than six carbon atoms. This patent also indicates that the esters have a certain ratio of the number percent of acyl groups that have 8 or more carbon atoms and are unbranched to the number percent of acyl groups that are branched and contain not more than 6 carbon atoms, and that this ratio is not greater than 1.56. Also, the patent requires that the number percent of acyl groups having at least 9 carbon atoms, branched or not branched, will be not greater than 81. PCT Application WO 90/12849 published November 1, 1990 by Jolley et al. discloses generally liquid compositions containing a major amount of at least one fluorine containing hydrocarbon containing one or two carbon atoms and a minor amount of at least one soluble organic lubricant comprising at least one carboxylic ester of a polyhydroxy compound containing at least two hydroxy groups and having the formula R[0C(O)R'] n where R is hydrocarbyl, each R' is independently hydrogen, straight chain lower hydrocarbyl, a branched chain hydrocarbyl group, or a straight chain hydrocarbyl group containing from 8 to about 22 carbon atoms, provided that at least one R' group is hydrogen, a lower straight chain hydrocarbyl or a branched chain hydrocarbyl group, or a carboxylic acid-containing or carboxylic acid ester-containing hydrocarbyl group, and n is at least 2. U.K. Patent 2,216,541, issued October 23, 1991, to Imperial Chemical Industries and published October 11, 1989, discloses the use of any ester of molecular weight 250 or greater as being suitable for use as compatible lubricants with Refrigerant 134a (R-134a) and some related refrigerant fluids. The patent exemplifies adipates, pyromellitates and benzoates. European Published Patent Application 440069 published August 7, 1991, by Kao Corporation discloses refrigeration working fluids composed of fluoroethanes and esters prepared by reacting an aliphatic polyol and a straight or branched chain alcohol with an aliphatic polycarboxylic acid having 2 to 10 carbon atoms. European Published Application 415778 published March 6, 1991, by Kao Corporation discloses refrigeration working fluid compositions containing hydrogenated fluoroethane and an ester compound obtained from an aliphatic polyhydric alcohol, a saturated aliphatic dicarboxylic acid and a saturated aliphatic monocarboxylic acid. European Published Application 406479 published January 9, 1991, by Kyodo Oil Technical Research Center Co., Ltd., discloses lubricants which are said to be compatible with R134a. Suitable lubricants are: esters of neopentyl glycol and a straight or branched- chain monovalent fatty acid having 3-18 carbon atoms; esters of pentaerythritol, dipentaerythritol and tripentaerythritol with straight or branched chain C2~ C ] _8 monovalent fatty acids; esters of a trihydroxy polyvalent alcohol of the formula RC(CH20H)3 where R is C1-C3 alkyl with a straight or branched-chain monovalent fatty acid having 2-18 carbon atoms and not more than 25 mol% per total fatty acid of at least one polybasic acid having carbon number of 4-36. European Published Application 435253 published July 3, 1991, by Nippon Oil Co., Ltd. discloses a number of esters said to be compatible with R134a, the esters being defined as having specific structures and being esters of mono-, di- and tri-pentaerythritol and other polyols such as trimethylolethane, trimethylolpropane, tri ethylolbutane or dimers or trimers thereof with monocarboxylic acids having 2-15 carbon atoms and dicarboxylic acids having 2-10 carbon atoms. The esters are generally said to have molecular weights of about 200-3000. European Published Application 430657 published June 5, 1991, by Ashai Denka Kogyo Kabushiki discloses lubricants compatible with R134a which are characterized at being neopentyl polyol ester of a fatty acid having 2 to 6 carbon atoms. It is said in this publication that the use of acids having 7 or more carbon atoms will result in incompatibility if the amount of C2-C 5 acids is not 20 mol% or greater such that the average number of carbon atoms of the fatty acids per hydroxyl group of the neopentylpolyol is 6 or below. Suitable neopentyl polyols include mono-, di- and tri- pentaerythritol, trimethylolpropane, and trimethylolethane. The polyols must have at least 3 OH groups. In the operation of a typical refrigeration system, the working fluid composition comprising a mixture of refrigerant and lubricant is passed from the compressor, where the temperatures are highest and where the lubricant is needed, to the condenser, where temperatures are reduced. Thereafter, the working fluid composition is then sent on to the evaporator, where temperatures are coldest and where the lubricant is not needed. Thereafter the working fluid composition, in vapor form, is returned to the compressor for repetition of the cycle. The refrigerant working fluid compositions of this invention will exhibit partial or complete homogeneity and irascibility of the ester lubricant and the HFC refrigerant blends when the working fluid composition is in the evaporator, but when the working fluid composition is in the compressor, where temperatures are high and lubricant is needed, the ester lubricant in a very concentrated form is available for lubrication of the compressor since the ester lubricant and the refrigerant blends exhibit complete immiscibility at high temperatures, i.e., about 120°C to 180°C or greater. Thus, separation of the ester lubricant from the refrigerant blends in the compressor is beneficial. The working fluid compositions of this invention may also be partially miscible or semi-homogeneous at lower temperatures, i.e., the blend of ester and refrigerant may exhibit partial miscibility, but this partial miscibility or semi-homogeneity does not prevent their use in refrigeration equipment, and such semi-homogeneous compositions also exhibit substantially complete immiscibility at higher temperatures, i.e., at about 120°C to 180°C or greater, thereby capable of achieving the objectives of this invention. Therefore, the present inventors have discovered that miscibility/immiscibility can be significantly influenced by blending refrigerants. More importantly, however, is the fact that the present inventors have discovered that the temperature/immiscibility relationship of refrigerant blends such as R125, R143a and R134a, or R125 and R143a, is inverse to that of conventionally known single component refrigerants with polyol esters. The present inventors have found that when the specific refrigerant blends of the present invention are mixed with polyol ester lubricants, the lubricants become immiscible at high temperatures allowing for separation of refrigerant and lubricant in the compressor section of a cooling system which operates at high temperatures, thereby allowing a certain portion of the lubricant to remain behind in the compressor section rather than cycling through the entire cooling system where the lubricant is not needed. To the contrary, single refrigerants such as R134a and R143a are immiscible at lower temperatures allowing for separation of refrigerant and lubricant in the evaporator section of the cooling system which operates at low temperatures, thereby allowing a certain portion of the lubricant to remain behind in the evaporator section where the lubricant is not needed and thereby depriving the compressor section of the much needed lubricant (See Figs. 3 and 4). A single refrigerant such as R125 is also undesirable since it is miscible at all temperatures which the cooling system operates, thereby causing the lubricant to pass from evaporator to compressor to condenser, in series, without the benefit of concentration and separation of an immiscible polyol ester lubricant in the compressor section which is sought by using the refrigerant blends of the present invention (See Fig. 5). Still other refrigerants such as R32 are undesirable since they are miscible at high temperatures and immiscible at low temperatures (See Fig. 6). Such refrigerants cause the lubricant to separate out of the working fluid composition while in the evaporator section, thereby depriving the compressor section of the much needed lubricant. European Patent Publication No. 0 536 940, published on April 14, 1993, and assigned to Imperial Chemical Industries PLC discloses a working fluid comprising a heat transfer fluid comprising a mixture of at least two compounds selected from the group consisting of hydrofluoroalkanes and fluoroalkanes; and a lubricant. The heat transfer fluid may comprise two, three or more components selected from the group consisting of: R32, R134, R134a, R125, R152a, R143a and R143. One suitable heat transfer fluid comprises a mixture of R32 and R125. However, as demonstrated in Fig. 7, attached hereto, working fluid compositions which include a blend of R32 and R125 are not immiscible at higher temperatures, except for the composition having a lubricant of technical grade pentaerythritol, cekanoic 9 and cekonic 8 which exhibited immiscibility in the temperature range of between 100-130°C. If, however, you refer to Example E on Fig. 1, this lubricant is considered miscible at all temperatures in the refrigerant blend according to the present invention and in Example I on Fig. 2, this lubricant is considered immiscible from 120-180°C. Therefore, it quite clear that not all refrigerant blends act the same and that each blend of refrigerants exhibits its own unique miscibility and immiscibility properties. Thus, it would not be obvious to one of ordinary skill in the art what affect one combination of refrigerant blends would have on the miscibility of a particular polyol ester lubricant, based upon the teaching of other refrigerant blends such as that demonstrated in the Fig. 7. Therefore, since European Patent Publication No. 0 536 940 does not disclose the specific weight percents of the unique refrigerant blends (especially that of R134a) recited in the present invention nor the specific lubricants admixed with such blends, it cannot be conclusively stated that they would exhibit the same miscibility and immiscibility properties of the refrigeration working fluid composition of the present invention. One cannot readily determine from the miscibility data of a single refrigerant and lubricant what affect the blending of another refrigerant together with that single refrigerant would have on the miscibility properties of the resulting working fluid without the benefit of the extensive research efforts of the present inventors. Leaving the lubricant behind in the compressor maximizes the lubricant's effect while leaving it behind in the evaporator minimizes its effect. Therefore, it was completely unexpected that when blending selected refrigerants, which by themselves do not behave in such a way that the lubricant is immiscible in high temperature environments such as a compressor and miscible in low temperature environments such as an evaporator, enhanced lubrication of a cooling system can occur. SUMMARY OF THE INVENTION In accordance with the present invention there have been discovered blends of HFC refrigerants and polyol esters of certain monocarboxylic acids useful as refrigeration working fluids exhibiting reverse miscibility which provide improved lubrication of refrigeration equipment containing such compositions. The preferred working fluid compositions according to the present invention are as follows: (a) A refrigeration working fluid composition which is miscible or partially miscible at temperatures of less than 120°C and which is immiscible at temperatures of at least about 120-180°C or greater, the refrigeration working fluid comprising: (i) about 65 to 95 weight % of a refrigerant, based on the total weight of the working fluid composition, the refrigerant comprising a blend of pentafluoroethane, 1, 1, 1-trifluoroethane, and 1,1,1,2- tetrafluoroethane, wherein the tetrafiuoroethane is present in an amount of between about 0.5 to 10 weight %, based on the total weight of the refrigerant, and (ϋ) about 5 to 35 weight % of a polyol ester lubricant, based on the total weight of the working fluid composition. (b) A refrigeration working fluid composition which is miscible or partially miscible at temperatures of less than 120°C and which is immiscible at temperatures of at least about 120-180°C, the refrigeration working fluid comprising: (i) about 65 to 95 weight % of a refrigerant, based on the total weight of the working fluid composition, the refrigerant comprising a blend of 1, 1, 1-trifluoroethane and pentafluoroethane, and (ii) about 5 to 35 weight % of a polyol ester lubricant, based on the total weight of the working fluid composition. - l i ¬ lt is a further object of the present invention wherein a mechanical vapor recompression type cooling system comprising an evaporator, a compressor, and a condensor has refrigeration working fluid compositions (a) and (b) cycling therethrough, wherein the refrigeration working fluid composition is miscible or partially miscible in the evaporator at temperatures of less than 120°C and immiscible in the compressor at temperatures of at least about 120-180°C, whereby the polyol ester lubricant is separated from the refrigerant in the compressor when lubricant the is most needed and the polyol ester lubricant is miscible or partially miscible in the refrigerant while the refrigeration working fluid composition is contained in the evaporator such that the polyol ester lubricant can be readily transported from the evaporator to the compressor. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a chart which show the reversible miscibility exhibited by the refrigeration working fluid composition of the present invention comprising a refrigerant of 44% R125, 52% R143a and 4% R134a and the selected polyol ester lubricants verses refrigeration working fluid compositions which do not exhibit reversible miscibility; Fig. 2 is a chart which show the reversible miscibility exhibited by the refrigeration working fluid composition of the present invention comprising a refrigerant of 55% R143a and 45% R125 and the selected polyol ester lubricants verses refrigeration working fluid compositions which do not exhibit reversible miscibility; Fig. 3 is a chart which shows the relative immiscibility of various polyol ester lubricants in R143a at any temperature; Fig. 4 is a chart which shows the relative miscibility of various polyol ester lubricants in R134a at any temperature; Fig. 5 is a chart which shows the relative miscibility of various polyol ester lubricants in R125 at any temperature and the relative immiscibility of other polyol ester lubricants in R125 at any temperature; Fig. 6 is a chart which shows the reversible miscibility of various polyol ester lubricants in R32, wherein these lubricants are immiscible at low temperatures and miscible at higher temperatures which is completely inopposite to the present invention; and Fig. 7 is a chart which shows the relative miscibility of various polyol ester lubricants in a refrigerant blend of 60 weight % R32 and 40 weight % R125 at any temperature, except for working fluids which are formed using TPE/CK9/CK8 which exhibited immiscibility in the narrow temperature range of between about 100-130°C. DETAILED DESCRIPTION OF THE INVENTION The polyol esters are present in an amount effective to provide lubrication, which is generally over the range of about 5-35% by weight based on the total weight or the refrigeration working fluid composition. Preferred amounts are 10%, 25% and 35% ester. The refrigeration working fluid compositions of this invention are preferably either: (a) a refrigeration working fluid composition which is essentially a homogeneous or semi-homogeneous one phase composition at low temperatures but which exhibits immiscibility at temperatures of about 120- 180°C comprising (i) a refrigerant composed of a blend of 44 wt.% R-125, 52 wt.% R-143a, and 4 wt.% R-134a, and an effective amount of (ii) a polyol ester lubricant being (1) a trimethylolpropane ester of (a) 3,5,5-trimethylhexanoic acid, (b) a mixture of 67 % by weight n-heptanoic acid with 24 % by weight 2- methylhexanoic acid, 7 % by weight 2-ethylpentanoic acid and 2 % by weight mixed isomers of C alkanoic acids or (c) a mixture of heptanoic acids composed of about 25 wt.% 3, 4-dimethylpentanoic, 51% 3,4 and 5- methylhexanoic, 8% n-heptanoic, 5% 3-ethylpentanoic and the balance a mixture of other branched heptanoic acids, or (2) a technical grade pentaerythritol ester of (a) branched C 7 acids being a mixture of 27 wt.% 2- ethylpentanoic acid, 74 wt.% 2-methylpentanoic acid and the balance mixed C 7 acid isomers or (b) n-pentanoic acid; or (b) a refrigeration working fluid which is essentially a homogeneous or semi-homogeneous one phase composition at low temperatures but which exhibits immiscibility at temperature of 120-180SC comprising (a) a refrigerant composed of a mixture of 55-50 wt.% R-143a, and 45-50 wt.% R-125, and an effective amount of (b) a polyol ester lubricant being (1) a trimethylolpropane ester of (a) 2-ethyl hexanoic acid, (b) 3,5,5-trimethylhexanoic acid or (c) a mixture of branched heptanoic acids composed of 25 wt.% 3,4- di ethylpentanoic, 51% 3,4 and 5-methylhexanoic, 8% n- heptanoic, 5% 3-ethylpentanoic and the balance a mixture of other branched heptanoic acids; (2) a technical grade pentaerythritol ester of (a) a mixture of about 75 wt.% 3,5,5-trimethylhexanoic acid and about 25 wt.% of a branched chain C Q carboxylic acid mixture composed of 25 wt.% 3,5-dimethylhexanoic acid, 19 wt.% 4,5-dimethyl-hexanoic acid, 17% 3,4-dimethylhexanoic acid, 11% 5-methylheptanoic acid, 5 wt.% 4- methylheptanoic acid and the balance mixed methylheptanoic and di ethylhexanoic acids, (b) n- pentanoic acid, or (c) a mixture of heptanoic acids composed of about 25% 3,4-dimethylpentanoic, 51% 3,4 and 5-methylhexanσic, 8% n-heptanoic, 5% 3- ethylpentanoic and the balance a mixture of other branched heptanoic acids. As used herein, R125 refers to pentafluoroethane, R143a refers to 1, 1, 1-trifluoroethane and R134a refers to 1, 1, 1,2-tetrafluoroethane. Miscibility and immiscibility is determined in the following manner. A measured quantity of ester lubricant is poured into a valved glass tube of 12 mm I.D. The tube is connected to a R-134a refrigerant charging unit, where air is evacuated and a set volume of refrigerant is condensed into the glass tube until a desired refrigerant gas pressure drop is obtained. The composition of the lubricant/refrigerant mixture is calculated from weight measurements taken of the tube, tube plus lubricant, and tube plus lubricant plus refrigerant. The tube containing the lubricant/refrigerant is visually observed for miscibility at room temperature, in a high temperature visibility bath where the temperature is thermostatically controlled up to +180°C, and in a low temperature visibility bath where the temperature is thermostatically controlled down to -80°C. The mixture is considered miscible to a given temperature if one clear layer is observed. The mixture is considered immiscible if two separate layers are observed. Partial miscibility is any state between miscibility and immiscibility. In the data included in the examples, miscibility temperature refers to the lowest temperature at which miscibility is observed at the given composition. The highest of these temperatures is the miscibility value for working fluid compositions having that ester lubricant. EXAMPLES This invention is illustrated by Figures 1 and 2 which show the reversible miscibility exhibited by the compositions of the invention in plots which are composites for data obtained over three compositional ranges for each ester, i.e., 10%, 25% and 35% by weight ester. All percentages are by weight. Temperatures are in degrees centigrade. These examples produce an interesting phenomenon. Instead of having immiscibility in the lower temperatures ranges, as is often seen with the single components such as R143a, immiscibility now tends to occur in the higher temperature ranges which is highly desirable for cooling systems. The below examples produced a variety of working fluids which exhibited miscibility at low temperatures and immiscibility at high temperatures. Low temperature miscibility means that the lubricant will not separate out in the coldest parts of a cooling system, i.e., parts of the system where lubricant build-up could be detrimental to performance. Likewise, high temperature immiscibility means that the lubricant/refrigerant will separate in high temperature regions of the cooling system, such as the compressor, precisely where lubricant/refrigerant separation is most desirable. Figs. 1 and 2 also demonstrate that increased miscibility can be achieved by mixing refrigerants in the same way that it is achieved by mixing lubricants. The incompatibility R143 with polyol esters is almost eliminated when it is mixed with R125, even when R125 is the minority (i.e., less than 50%) component. In Figure 1, the compositions of the present invention, i.e., Examples B, C, and D, contain the esters identified below: B: TMP/CK9 - trimethylolpropane ester of 3,5,5- trimethylhexanoic acid ("Cekanoic 9 acid") C: TMP/1770 - trimethylolpropane ester of a mixture of acids being 67% n-heptanoic; 24% 2-methyl hexanoic, 7% 2-ethylpentanoic and 2% mixed isomers of Cη acids. D: TPE/CK7 - trimethylolpropane ester of mixed heptanoic acids ("Cekanoic 7 acid") which is a mixture of 23% 2-ethylpentanoic acid, 74% 2-methylhexanoic acid and the balance other C 7 acid isomers. Comparative compositions A and E contain refrigerant blends of 44% R125, 52% R143a and 4% R134a admixed with the following esters: A: Neopentyl glycol ester of 3,5,5- trimethylhexanoic acid. E: technical grade pentaerythritol ester of a mixture of (a) 85 wt.% 3, 5, 5-trimethylhexanoic and (b) 15 wt.% isooctanoic acids which is a mixture of 26 wt.% 3,5-dimethyl-, 19% 4,5-dimethyl, 17% 3,4- dimethylhexanoic acid, 11% 5-methylheptanoic, 5% 4- methylheptanoic and the balance mixed methylheptanoic and dimethylhexanoic acids. In Figure 2, the compositions of the invention are compositions F, G and I containing these esters: F: is the trimethylolpropane ester of 2-ethyl hexanoic acid. G: Is same ester as in composition B. I: is same ester as in composition E except there is used 75 wt.% of 3, 5, 5-trimethylhexanoic acid and 25% of the same mixture of isooctanoic acids. Comparative composition H contains refrigerant blends of 55% R143a and 45% R125 admixed with the following ester: H: TMP/1770 - trimethylolpropane ester of a mixture of acids being 67% n-heptanoic; 24% 2-methyl hexanoic, 7% 2-ethylpentanoic and 2% mixed isomers of C 7 acids. All esters were evaluated at the concentration levels of 10%, 25% and 35% by weight ester, based on the total weight of ester and refrigerant by weight based on the total weight of the refrigeration working fluid composition. The following additional compositions were evaluated over compositional ranges of 10%, 25% and 35% by weight ester with similar results: Composition J: The trimethylol propane ester of a mixture of heptanoic acids (25% 3 , 4-dimethylpentanoic, 51% 3,4 and 5-methylhexanoic acids, 8% n-heptanoic, 5% 3-ethylpentanoic and the balance a mixture of other branched heptanoic acids) was mixed with a blend of 44% R-125, 52% R-143a and 4% R-134a and was found to be miscible at -50°C to +58°C and immiscible at higher temperatures. Composition K: The technical grade pentaerythritol ester of n-pentanoic acid was evaluated with the same refrigerant blend as was Ester J and was found to be miscible at -50°C to +63°C and immiscible at higher temperatures. Composition L: The same ester used in Composition J was mixed with a blend of 50% by weight 143a and 50% by weight R-125 and was found miscible at -50°C to +55°C and immiscible at higher temperatures. Composition M: The same ester used in Composition K was mixed with the same refrigerant blend of Composition L and found to be miscible at -50°C and +61°C but immiscible at higher temperatures. Composition N: The technical grade pentaerythritol ester of the acid mixture of Composition J was mixed with the same refrigerant blend of Composition L and found to be miscible at -50°C and +32°C, but immiscible at higher temperatures.

Claims: What is Claimed is: 1. A refrigeration working fluid composition which is miscible or partially miscible at temperatures of less than 120°C and which is immiscible at temperatures of at least about 120-180°C, said refrigeration working fluid comprising: (i) about 65 to 95 weight % of a refrigerant, based on the total weight of said working fluid composition, said refrigerant comprising a blend of pentafluoroethane, 1, 1, 1-trifluoroethane, and 1,1,1,2- tetrafluoroethane, wherein said tetrafiuoroethane is present in an amount of between about 0.5 to 10 weight %, based on the total weight of the refrigerant, and (ii) about 5 to 35 weight % of a polyol ester lubricant, based on the total weight of said working fluid composition. 2. The composition according to claim 1 wherein said refrigerant comprises a blend of 44 weight % pentafluoroethane, 52 weight % 1, 1, 1-tri luoroethane, and 4 weight % 1, 1, 1,2-tetrafluoroethane. 3. The composition according to claim 1 wherein said polyol ester lubricant is selected from the group consisting of: (1) an esterification reaction product of trimethylolpropane and at least one acid or acid mixture selected from the group consisting of: (a) 3,5, 5-trimethylhexanoic acid, (b) a mixture of 67 % by weight n- heptanoic acid with 24 % by weight 2-methylhexanoic acid, 7 % by weight 2-ethylpentanoic acid and 2 % by weight mixed isomers of C7 alkanoic acids, and (c) a mixture of heptanoic acids composed of about 25 wt.% 3, 4-dimethylpentanoic, 51% 3,4 and 5-methylhexanoic, 8% n-heptanoic, 5% 3- ethylpentanoic and the balance a mixture of other branched heptanoic acids; and (2) an esterification reaction product of technical grade pentaerythritol ester and at least one acid or acid mixture selected from the group consisting of: (a) branched C 7 acids being a mixture of 27 wt.% 2-ethylpentanoic acid, 74 wt.% 2- methylpentanoic acid and the balance mixed C 7 acid isomers, and (b) n-pentanoic acid. 4. A refrigeration working fluid composition which iε miscible or partially miscible at temperatures of less than 120°C and which is immiscible at temperatures of at least about 120-180°C, said refrigeration working fluid comprising: (i) about 65 to 95 weight % of a refrigerant, based on the total weight of said working fluid composition, said refrigerant comprising a blend of 1, 1, 1-trifluoroethane and pentafluoroethane, and (ii) about 5 to 35 weight % of a polyol ester lubricant, based on the total weight of said working fluid composition. 5. A composition according to claim 4 wherein said refrigerant comprises a blend of 50-55 wt. % 1, 1, 1-trifluoroethane and 45-50 weight % pentafluoroethane. 6. The composition according to claim 4 wherein said polyol ester lubricant is selected from the group consisting of: (1) an esterification reaction product of trimethylolpropane and at least one acid or acid mixture selected from the group consisting of: (a) 2-ethyl hexanoic acid, (b) 3,5, 5-trimethylhexanoic acid, and (c) a mixture of branched heptanoic acids comprising 25 weight % 3 , 4-dimethylpentanoic, 51 weight % 3,4 and 5-methylhexanoic, 8 weight % n- heptanoic, 5 weight % 3-ethylpentanoic and the balance a mixture of other branched heptanoic acids; and (2) an esterification reaction product of technical grade pentaerythritol ester and at least one acid or acid mixture selected from the group consisting of: (a) a mixture of about 75 weight % 3,5, 5-trimethylhexanoic acid and about 25 weight % of a branched chain C 8 carboxylic acid mixture composed of 25 weight % 3,5-dimethylhexanoic acid, 19 weight % 4,5- dimethylhexanoic acid, 17 weight % 3,4- dimethylheptanoic acid, 11 weight % 5-methylheptanoic acid, 5 weight % 4-methylheptanoic acid and the balance mixed methylheptanoic and dimethylhexanoic acids, (b) n-pentanoic acid, and (c) a mixture of heptanoic acids comprising: about 25 weight % 3, 4-dimethylpentanoic, 51 weight % 3,4 and 5-methylhexanoic, 8 weight % n- heptanoic, 5 weight % 3-ethylpentanoic and the balance a mixture of other branched heptanoic acids. 7. A mechanical vapor recompression type cooling system comprising an evaporator, a compressor, and a condensor, wherein said cooling system includes a refrigeration working fluid composition which cycles therethrough, said refrigeration working fluid composition is miscible or partially miscible in said evaporator at temperatures of less than 120°C and immiscible in said compressor at temperatures of at least about 120-180°C, said refrigeration working fluid comprising: (i) about 65 to 95 weight % of a refrigerant, based on the total weight of said working fluid composition, said refrigerant comprising a blend of pentafluoroethane, 1, 1, 1-trifluoroethane, and 1, 1, 1, 2-tetrafluoroethane, wherein said tetrafiuoroethane is present in an amount of between about 0.5 to 10 weight %, based on the total weight of the refrigerant, and (ii) about 5 to 35 weight % of a polyol ester lubricant, based on the total weight of said working fluid composition, whereby said polyol ester lubricant is separated from said refrigerant in said compressor when lubricant is most needed and said polyol ester lubricant is miscible or partially miscible in said refrigerant while said refrigeration working fluid composition is contained in said evaporator such that said polyol ester lubricant can be readily transported from said evaporator to said compressor. 8. The cooling system according to claim 7 wherein said refrigerant comprises a blend of 44 weight % pentafluoroethane, 52 weight % 1, 1, 1-trifluoroethane, and 4 weight % 1, 1, 1,2-tetrafluoroethane. 9. The cooling system according to claim 7 wherein said polyol ester lubricant is selected from the group consisting of: (1) an esterification reaction product of trimethylolpropane and at least one acid or acid mixture selected from the group consisting of: (a) 3,5,5-trimethylhexanoic acid, (b) a mixture of 67% by weight n- heptanoic acid with 24% by weight 2-methylhexanoic acid, 7% by weight 2-ethylpentanoic acid and 2% by weight mixed isomers of C 7 alkanoic acids, and (c) a mixture of heptanoic acids composed of about 25 wt.% 3, 4-dimethylpentanoic, 51% 3,4 and 5-methylhexanoic, 8% n-heptanoic, 5% 3- ethylpentanoic and the balance a mixture of other branched heptanoic acids; and (2) an esterification reaction product of technical grade pentaerythritol ester and at least one acid or acid mixture selected from the group consisting of: (a) branched C 7 acids being a mixture of 27 wt.% 2-ethylpentanoic acid, 74 wt.% 2- methylpentanoic acid and the balance mixed C 7 acid isomers, and (b) n-pentanoic acid. 10. A mechanical vapor recompression type cooling system comprising an evaporator, a compressor, and a condensor, wherein said cooling system includes a refrigeration working fluid composition which cycles therethrough, said refrigeration working fluid composition is miscible or partially miscible in said evaporator at temperatures of less than 120°C and immiscible in said compressor at temperatures of at least about 120-180°C, said refrigeration working fluid comprising: (i) about 65 to 95 weight % of a refrigerant, based on the total weight of said working fluid composition, said refrigerant comprising a blend of 1, 1, 1-trifluoroethane and pentafluoroethane, and (ii) about 5 to 35 weight % of a polyol ester lubricant, based on the total weight of said working fluid composition, whereby said polyol ester lubricant is separated from said refrigerant in said compressor when lubricant is most needed and said polyol ester lubricant is miscible or partially miscible in said refrigerant while said refrigeration working fluid composition is contained in said evaporator such that said polyol ester lubricant can be readily transported from said evaporator to said compressor. 11. A cooling system according to claim 10 wherein said refrigerant comprises a blend of 50-55 wt. % 1, 1, 1-trifluoroethane and 45-50 weight % pentafluoroethane. 12. The cooling system according to claim 10 wherein said polyol ester lubricant is selected from the group consisting of: (1) an esterification reaction product of trimethylolpropane and at least one acid or acid mixture selected from the group consisting of: (a) 2-ethyl hexanoic acid, (b) 3, 5,5-trimethylhexanoic acid, and (c) a mixture of branched heptanoic acids comprising 25 weight % 3 , 4-dimethylpentanoic, 51 weight % 3,4 and 5-methylhexanoic, 8 weight % n- heptanoic, 5 weight % 3-ethylpentanoic and the balance a mixture of other branched heptanoic acids; and (2) an esterification reaction product of technical grade pentaerythritol ester and at least one acid or acid mixture selected from the group consisting of: (a) a mixture of about 75 weight % 3,5, 5-trimethylhexanoic acid and about 25 weight % of a branched chain C 8 carboxylic acid mixture composed of 25 weight % 3, 5-dimethylhexanoic acid, 19 weight % 4,5- dimethylhexanoic acid, 17 weight % 3,4- dimethylheptanoic acid, 11 weight % 5-methylheptanoic acid, 5 weight % 4-methylheptanoic acid and the balance mixed methylheptanoic and dimethylhexanoic acids, (b) n-pentanoic acid, and (c) a mixture of heptanoic acids comprising: about 25 weight % 3, 4-dimethylpentanoic, 51 weight % 3,4 and 5-methylhexanoic, 8 weight % n- heptanoic, 5 weight % 3-ethylpentanoic and the balance a mixture of other branched heptanoic acids.

Inventors: DUNCAN CAROLYN BOGGUS, KREVALIS MARTIN ANTHONY, SCHLOSBERG RICHARD HENRY, DUNCAN, CAROLYN, BOGGUS, KREVALIS, MARTIN, ANTHONY, SCHLOSBERG, RICHARD, HENRY
Applicants: EXXON CHEMICAL PATENTS INC, EXXON CHEMICAL PATENTS INC.
Application year: 1995
Main classification: C09K5
IPC codes: C09K5, C10M105, C10M171