AZEOTROPE-LIKE COMPOSITIONS OF PENTAFLUOROETHANE AND 1,1,1-TRIFLUOROETHANE

Abstract: Azeotrope-like compositions comprising pentafluoroethane and 1,1,1-trifluoroethane are stable and have utility as refrigerants for heating and cooling.

Description: DESCRIPTION AZEOTROPE-LIKE COMPOSITIONS OF PENTAFLUOROETHANE AND 1,1,1-TRIFLUOROETHANE Field of the Invention This invention relates to azeotrope-like or essentially constant-boiling mixtures of pentafluoroethane and 1,1,1- trifluoroethane. These mixtures are useful as refrigerants for heating and cooling. CROSS-REFERENCE TO RELATED APPLICATION Commonly assigned U.S. patent No. 4,944,388 discloses azeotrope-like mixtures of pentafluoroethane; 1,1,1- trifluoroethane; and chlorodifluoromethane. BACKGROUND OF THE INVENTION Fluorocarbon based fluids have found widespread use in industry for refrigeration applications such as air conditioning and heat pump applications. Vapor compression is one type of refrigeration. In its simplest form, vapor compression involves changing the refrigerant from the liquid to the vapor phase through heat absorption at a low pressure and then from the vapor to the liquid phase through heat removal at an elevated pressure. First, the refrigerant is vaporized in the evaporator which is in contact with the body to be cooled. The pressure in the evaporator is such that the boiling point of the refrigerant is below the temperature of the body to be cooled. Thus, heat flows from the body to the refrigerant and causes vaporization. The formed vapor is then removed by means of a compressor in order to maintain the low pressure in the evaporator. The temperature and pressure of the vapor are then raised through the addition of mechanical energy by the compressor. The high-pressure vapor then passes to the condenser whereupon heat exchange with a cooler medium, the sensible and latent heats are removed with subsequent condensation. The hot liquid refrigerant then passes to the expansion valve and is ready to cycle again. While the primary purpose of refrigeration is to remove energy at low temperature, the primary purpose of a heat pump iβ to add energy at higher temperature. Heat pumps ace considered reverse cycle systems because for heating, the operation of the condenser is interchanged with that of the ref igeration evaporator. Certain chloro luoro ethane and chlorofluoroethane derivatives have gained widespread use in refrigeration applications including air conditioning and heat pump applications owing to their unique combination of chemical and physical properties. The majority of refrigerants utilized in vapor compression systems ace either single components fluids or azeotropic mixtucββ. The use of azeotcopic mixtures as refrigerants iβ known in the act; foe example, see R. c. Downing. FLUOROCARBONS REFRIGERANTS HANDBOOK. Prentice- Hall. 1988 and U.S. Patents 2.101.993 and 2.641.579. R-502 iβ an azeotropic blend which consists of monochlorodifluoromethane(R-22) and chloropentafluoro- ethane(R-115) . a fully halogenated chlorofiuorocarbon. R-502 has been coutinely used foe medium to low tempecatuce cefcigecation applications. Azeotropic or azeotrope-like compositions are desired because they do not fractionate upon boiling. This behavior is desirable because in the previously described vapor compression equipment with which these refrigerants are employed, condensed material is generated in preparation for cooling or for heating purposes. Unless the refrigerant composition exhibits a constant boiling point, i.e. is azeotrope-like. fractionation and segregation will occur upon evaporation and condensation and undesirable refrigerant distribution may act to upset the cooling or heating. Non-azeotropic mixtures have been disclosed as refrigerants for example in U. S. Patent 4.303.536 but have not found widespread use in commercial applications. The use of non-azeotropic mixtures which fractionate during the ce cigecation cycle introduces additional complexity into the system which neceββitateβ hacdware changes. The use of non-azeotropic cefcigecants has been avoided pcimacily due to the added difficulty in charging and secvicing ce igecation equipment and the situation is fucthec complicated if an inadvertent leak in the system occucβ ducing use oc ducing service. The composition of the mixture could change affecting system pressures and system pecfocmance. If one component of the non- azeotcopic ixtucβ iβ flammable, then fcactionation could shift the composition into the flammable cegion with potential advecβe consequences. The act iβ continually seeking new fluococacbon based azeotcope-like mixtures which offer alternatives for refrigeration and heat pump applications. Cuccently, of pacticulac interest, ace fluococacbon based azeotcope-like mixtuces which ace considered to be environmentally safe substitutes for the presently used fully halogenated chlorofluorocarbons(CFCs) . The latter are suspected of causing environmental problems in connection with the earth's protective ozone layer. The substitute materials must also possess those properties unique to the CFCs including chemical stability, low toxicity, non-flammability. and efficiency in-use. The latter characteristic is important in refrigeration and air-conditioning especially where a loss in refrigerant thermodynamic performance or energy efficiency may have secondary environmental impacts through increased fossil fuel usage arising from an increased demand for electrical energy. Furthermore, the ideal CFC refrigerant substitute would not require major engineering changes to conventional vapoc compcession technology cuccently used with CFC refrigerants. Mathematical models have substantiated that hydrofluoro¬ carbons. such as pentafluoroethane(HFC-125) and 1,1.1- trifluoroethane(HFC-143a) will not advecβely affect atmospheric chemiβtcy. being negligible contcibutocs to ozone depletion and to green-house global wacming in comparison to the fully halogenated species. Because HFC-143a iβ as efficient aβ R-502 and provides a modest increase in cefcigecation capacity. HFC-143a might be conβideced a good cefcigecant βubβtitute foe R-502. Howβvβc. a diβadvantage of HFC-143a aβ a cefcigecant iβ that the vapoc of HFC-143a iβ flammable. Aβ a ceβult, the shipping, handling, and use of HFC-143a have to be cacefully controlled due to the potential flammability. Because HFC-125 iβ nonflammable and provides a modeβt increase in cefcigecation capacity compaced with R-502. HFC-125 might be consideced a good cefcigecant substitute for R-502.- However, a disadvantage of HFC-125 is that HFC-125 is about 5% less efficient than R-502. It is an object of this invention to provide novel azeotrope-like compositions based on pentafluoroethane and 1.1.1-trifluoroethane which will not fractionate under normal cooling or heating conditions. Another object of the invention is to provide novel environmentally acceptable refrigerants for use in the aforementioned applications. Other objects and advantages of the invention will become apparent from the following description. DESCRIPTION OF THE INVENTION In accordance with the invention, novel azeotrope- like compoβitionβ have been discovered comprising penta- fluoroethane and 1,1.1-trifluoroethane. The azeotrope- like compositionβ comprise from about 1 to about 80 weight percent pentafluocoethane and fcom about 20 to about 99 weight peccent 1.1.1-trifluoroethane which have a vapor pressure of about 167 pβia(1113 kPa) ± about 6 pβia(40 kPa) at 70°F(21.1*C). These compoβitionβ ace azeotcope- like because they ace constant-boiling, i.e. exhibit essentially conβtant-vapoc pressure versus composition and essentially identical liquid and vapoc compoβitionβ over the afocementioned compositional cangeβ. In a pcefecced embodiment of the invention, the azeotcope-like compoβitionβ of the invention compcise fcom about 38.4 to about 80 weight percent pentafluoroethane and fcom about 20 to about 61.6 weight peccent 1.1.1- tcifluocoethane. Vapoc phase compositionβ containing in excess of about 38.4 weight percent pentafluoroethane were determined to be nonflammable in air at ambient conditions using the ASTM E-681 method as specified in the American Society of Heating. Refrigerating, and Air-Conditioning Engineers(ASHRAE) Standard 34. In a most preferred embodiment of the invention, the azeotrope-like compositions of the invention comprise from about 40 to about 80 weight percent pentafluoroethane and from about 20 to about 60 weight percent 1.1.1- trifluoroethane. These compositions are constant-boiling, non-segregating, and nonflammable. These most preferred azeotrope-like compositions of the invention have a vapor pressure of about 167 pβia(1113 kPa) + about 4 pβia(27 kPa) at 70 β F(21.1 β C) . A blend of HFC-125 and HFC-143a was disclosed as having utility aβ a cefcigecant in RESEATCH DISCLOSURE 15402. Febcuacy 1977 but thiβ diβcloβuce implied that such a blend was non-azeotcopic. i.e. would fcactionate upon evapocation oc condensation, and stated that the blend was disadvantageous because it was flammable. Contcacy to thiβ teaching, we have discovered that the blende of HFC- 125 and HFC-143a aβ recited above ace both constant- boiling, i.e. azeotcope-like. and ace nonflammable. The teem N azeotcope-like N iβ uβed herein foe the ixtuceβ of the invention because in the claimed pcopoctionβ. .he compoβitionβ of pentafluocoethane and 1.1.1-trifluoroethane ace constant-boiling oc essentially constant-boiling. All compoβitionβ within the indicated ranges, as well as cectain compositionβ outβide the indicated ranges. are azeotrope-like. aβ defined mor<? particularly below. From fundamental principles, the thermodynamic state of a fluid is defined by four variables: pressure, temperature, liquid composition and vapor composition, or P-T-X-Y, respectively. An azeotrope is a unique characteristic of a system of two or more components where X and Y are equal at the stated P and T. In practice, this means that the components of a mixture cannot be separated during a phase change, and therefore are useful in the cooling and heating applications as described above. For the purpose of this discussion, azeotrope-like composition is intended to mean that the composition behaves like an azeotrope. i.e. has constant-boiling characteristics or a tendency not to fractionate upon boiling or evaporation. Thus, in βuch compoβitions, the composition of the vapor formed during boiling or evaporation iβ identical or substantially identical to the original liquid composition. Hence, during boiling or evapocation. the liquid composition, if it changes at all. changes only to a minimal oc negligible extent. This is to be contrasted with non-azeotrope-like compoβitions in which during boiling oc evapocation. the liquid composition changeβ to a substantial degcee. Thuβ. one way to detecmine whethec a candidate mixtuce iβ "azeotcope-like" within the meaning of this invention, iβ to distill a sample theceof undec conditions (i.e. ceβolution - number of plateβ) which would be expected to separate the mixture into its separate components. If the mixtuce iβ non-azeotcopic oc non- azeotrope-like. the mixture will fractionate, i.e. βepacate into its various components with the lowest boiling component distilling off first, and so on. If the mixture iβ azeotcope-like. some finite amount of a first distillation cut will be obtained which contains all of the mixture components and which is constant-boiling or behaves as a single substance. This phenomenon cannot occur if the mixture is not azeotrope-like i.e., it is not part of an azeotropic system. It follows from the above that another characteristic of azeotrope-like compositions is that there is a range of compositions containing the same components in varying proportions which are azeotrope-like or constant-boiling. All such compositionβ are intended to be covered by the term azeotrope-like or constant- boiling as used herein. As an example, it is well known that at differing pressures, the composition of a given azeotrope will vary at least slightly aβ does the boiling point of the composition. Thus, an azeotrope of A and B represents a unique type of relationship but with a variable composition depending on temperature and/or pressure. Aβ iβ readily understood by persons skilled in the act. the boiling point of the azeotcope will vacy with the pressure. In one process embodiment of the invention, the azeotrope-like compositio n s of the invention may be used in a method foe pcoducing refrigeration which comprises condensing a cefcigecant comprising the azeotcope-like compoβitionβ and thβceafter evapocating the cefcigecant in the vicinity of a body to be cooled. In anothec process embodiment of the invention, the azeotcope-like compoβitionβ of the invention may be used in a method foe pcoducing heating which compciβeβ condensing a cefcigecant compciβing the azeotcope-like compoβitionβ in the vicinity of a body to be heated and theceaftec evapocating the cefcigecant. The pentafluoroethane and 1.1,1-trifluoroethane of the novel azeotrope-like compositions of the invention are known materials. Preferably, the materials should be used in sufficiently high purity so as to avoid the introduction of adverse influences upon the cooling or heating properties or constant-boiling properties of the system. It should be understood that the present compositionβ may include additional components so as to form new azeotrope-like compositions. Any such compositions are considered to be within the scope of the present invention as long as the compositionβ are constant- boiling or essentially constant-boiling and contain all of the essential components desccibed hecein. The pceβent invention iβ moce fully illustrated by the following non-limiting Examples. EXAMPLE 1 Thiβ example shows that cectain compoβitionβ of pentafluocoethane and 1.1.1-trifluoroethane ace azeotrope- like. i.e. exhibit essentially identical liquid and vapor compoβitionβ. and ace constant-boiling, i.e. exhibit essentially conβtant vapoc pressure vecβuβ composition within thiβ cange. Vapoc liquid equilibcium experiments wece performed by pcepacing mixtures of HFC-125 and HFC-143a in an appcoximately 150 cubic centimetec vessel. The vessel, equipped with a magnetically dciven βticcec and a 0-300 psia(0-2068 kPa) pceββuce tcanβducec accucate to +0.2 . waβ βubmecged in a conβtant tempecatuce bath contcolled to within + 0.05 β F(0.03 β C) . Once thecmal equilibcium was attained, as determined by constant vapor pressure readings, vapor and liquid samples were withdrawn from the vessel and analyzed by standard gas chromatographic techniques. This procedure was repeated at three nominal compositions of about 25, 50, and 75 weight percent HFC-125 in HFC-143a. and at three temperatures of -1C "(-23.3°C). 70 β F(21.1°C). and 112.5 β F(44.7 β C) . Table I summarizes the results of these experiments. In Table I. the compositions are in weight percent HFC-125 in HFC-143a. The data shown in Table I indicate that the vapor and liquid compoβitionβ are eββentially identical within the experimental uncertainty of +1.0 weight peccent unit associated with the chcomatogcaphic analysis. The vapoc pressures of the blende are eββentially conβtant to within +2* over the composition range fcom about 1 to about 80 weight peccent HFC-125 and fcom about 99 to about 20 weight peccent HFC-143a, i.e. these blende ace constant-boiling oc azeotcope-like. EXAMPLE 2 This example shows that certain HFC-125/HFC-143a blends are nonflammable. Flammability measurements were performed using the ASTM E-681 technique modified according to ASHRAE Standard 34. Briefly, this technique involves preparing fluorocarbon/air gas mixtures to a total pressure of one atmosphere(lOlkPa) in a 5-liter spherical glass vessel, stirring the mixture with a magnetically driven propeller to ensure a uniform composition, and then attempting to ignite the mixture using an electrically activated kitchen match head as the ignition source. A ternary flammability diagram was mapped by preparing mixtures of HFC-125, HFC-143a. and air by the method of partial pressures and then determining whether or not a flame would propagate as defined by ASTM E-68 . The critical flammability composition, i.e. the composition of the HFC-125/HFC-143a blend which contains the maximum pcopoction of the flammable HFC-143a but does not exhibit flame limits in aic. waβ detecminβd in a gcaphical mannec βi ilac to that described in Haenni et al. Industrial and Engineering Chemiβtrv 51. 685(1959). The critical flammability compoβition waβ found to be 61.6 weight peccent HFC-1 3a and about 38.4 weight peccent HFC-125. In other words, blende of HFC-125 and HFC-143a containing 38.4 or more weight peccent HFC-125 ace nonflammable in all pcopoctions in aic at ambient conditions. EXAMPLE 3 Thiβ example shows that a blend of 50 weight percent HFC-125 and 50 weight percent HFC-143a undergoes essentially no fractionation and maintains a conβtant- vapor pressure during a vapor leak which illustrates one advantage of a constant-boiling or azeotrope-like composition. The vessel described in Example 1 was charged with approximately 105 grams of a 50/50 weight percent mixture of HFC-125 and HFC-143a. Vapor was allowed to leak from this container until about 14 weight percent of the original charge had dissipated, at which point the vapor pcessuce of the cemaining liquid was measuced and a vapor phase sample collected for analysis. The vapor leak was continued until 80% of the original charge had dissipated; additional vapor samples were taken for analysis at different stages during the leak. The temperature of the veββel waβ maintained at 70°F(21.1°C) during the leak. Vapor pressure and compoβition data are reported in Table II. In Table II. the compoβition iβ in weight percent HFC-125 in HFC-143a. TABLE II FRACTIONATION DATA The data liβted in Table II βhow that the compoβition of the mixture vacies by no oce than 1.2 weight peccent and that the vapoc pceββuce ce ainβ conβtant within 4psia (27 kPa) oc about 2.5% of the total pceββuce. EXAMPLE 4 This example shows that constant-boiling HFC-125/ HFC-l43a blends have certain advantages when compared to other refrigerants which are currently used in certain refrigeration cycles. The theoretical performance of a refrigerant at specific operating conditions can be estimated from the thermodynamic properties of the refrigerant using standard refrigeration cycle analysis techniques; see for example, R. C. Downing. FLUOROCARBONS REFRIGERANTS HANDBOOK. Chapter 3, Prentice-Hall, 1988. The coefficient of performance(COP) is a universally accepted measure, especially useful in representing the relative thermodynamic efficiency of a refrigerant in a specific heating or cooling cycle involving evapocation oc condensation of the cefcigecant. In cefcigecation engineecing, thiβ teem expresses the catio of useful cefcigecation to the enecgy applied by the compcessoc in compressing the vapor. The capacity of a refrigerant represents the volumetcic effectiveneββ of the cefcigecant. To a compcessoc engineec. thiβ value expresses the capability of a compceββoc to pump quantities of heat foe a given volumetcic flow cate of cefcigecant. In othec words, given a specific compressor, a cefcigecant with a highec capacity will delivec moce cooling oc heating powec. we have performed thiβ type of calculation for a medium to low tempecatuce cefcigecation cycle whece the condenser tempecatuce is typically 100*F(38°C) and the evapocatoc tempecatuce is typically -40 to -10*F(-40 to -23.3°C). We have fucthec assumed iβentcopic compression and a compressor inlet temperature of 65°F(18.3°C) . Such calculations were pecfocmed foe a 60/40 by weight peccent blend of HFC-125 and HFC-143a as well as for R-502. Table III lists the COP of a 60/40 blend of HFC-125 and HFC-143a relative to that of R-502 over a range of evaporator temperatures. In Table III. the * indicates that COP and capacity are given relative to R-502. TABLE III THERMODYNAMIC PERFORMANCE R-502 125/143a Evaporator Discharge Discharge Tem . Temp . Temp . COP* Capacity* • F( » C) • F( *C) -40(-40) 1.01 1.08 235(113) 213(101) -30(-34) 1.00 1.07 220(104) 200(93) -20(-29) 0.99 1.07 205(96) 189(87) -10(-23) 0.99 1.06 192(89) 177(81) The data listed in Table III show that the HFC-125/HFC-143a blend provides eββentially the βame COP(within +1%) aβ that attainable with R-502. provides about a 7% incceaβe in cefcigecation capacity, and also produces lowec diβchacge tempecatuces fcom the compressor, which contcibuteβ to compceββoc reliability. It has been recommended that compceββoc diβchacge tempecatuces be limited to about 225*F(107.2°C). Thiβ tempecatuce is exceeded in the cuccent example by R-502 at evapocatoc tempecatuce* lovec than -35 β F(-37.2*C): the HFC-125/ HFC-1 3a blend can opecate down to an evapocatoc tempecatuce of -50*F(-45.6°C) befoce exceeding the 225*F(107.2*C) diβchacge tempecatuce limit. Even lowec evapocatoc te pecatuceβ could be accompliβhed by enciching the HFC-125 component up to 80% of the total mixtuce. without significant impact on the pecfocmance. Having deβccibed the invention in detail and by cefecence to pcefecced embodimentβ theceof. it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

Claims: What is claimed is; 1. Azeotrope-like compositions comprising from 60 to 38.4 weight percent pentafluoroethane and from 40 to 61.6 weight percent 1,1,1-trifluoroethane which have a vapor pressure of 167 psia + 6 psia at 70°F. * 2. Azeotrope-like compositions according to claim 2 comprising 53.7 weight percent + 4 weight percent pentafluoroethane and 46.3 weight percent 1,1,1-trifluoroethane + 4 weight percent. 3. Azeotrope-like compositions according to claim 1 comprising from 51 to 38.4 weight percent pentafluoroethane and from 49 to 61.6 weight percent 1,1,1-trifluoroethane. 4. Azeotrope-like compositions according to claim 3 comprising 51 weight percent pentafluoroethane and 49 weight percent 1,1,1-trifluoroethane. 5. Azeotrope-like compositions according to claim 3 comprising 40 weight percent pentafluoroethane and 60 weight percent 1,1,1-trifluoroethane. 6. Azeotrope-like compositions according to claim 3 comprising 49 weight percent pentafluoroethane and 51 weight percent 1,1,1-trifluoroethane. 7. A method for producing refrigeration which comprises condensing a refrigerant comprising an azeotrope-like composition as described in any of the preceding claims evaporating said refrigerant in the vicinity of a body to be cooled. 8. A method for producing heat which comprises condensing a refrigerant comprising an azeotropic composition as described in claims 1 through 6 in the vicinity of a body to be heated and thereafter evaporating said refrigerant.

Inventors: ATWOOD THEODORE, LUND EARL A E, PHAM HANG THANH, SHANKLAND IAN R, ATWOOD, THEODORE, LUND, EARL, A., E., PHAM, HANG, THANH, SHANKLAND, IAN, R.
Applicants: ALLIED SIGNAL INC, ALLIED-SIGNAL INC.
Application year: 1993
Main classification: C09K5
IPC codes: C09K5