MIXTURES OF PENTAFLUOROETHANE AND TRIFLUOROETHANE

Abstract: Azeotropic compositions of 5-45 weight percent pentafluoroethane and 55-95 weight percent 1,1,1-trifluoroethane boil at -16.9 C and a pressure of about 51 psia. These compositions are useful as refrigerants, aerosol propellants, heat transfer media, gaseous dielectrics, fire extinguishing agents, expansion agents for polyolefins and polyurethanes and as power cycle working fluids.

Description: TITLE MIXTURES OF PENTAPLUOROETHANE AND TRIFLUOROETHANE BACKGROUND OF THE INVENTION This invention relates to azeotropic compositions of pentafluoroethane and 1,1,1-trifluoroethane. Recently the long-term environmental effects of chlorofluoro- carbons have come under scientific scrutiny, because it has been postulated that these materials because of their high stability are able to reach the stratosphere where under the influence of ultraviolet radiation release chlorine atoms which, in turn, undergo chemical reaction in the stratospheric ozone. Reduction of stratospheric ozone would increase the amount of ultraviolet radiation reaching the earth's surface. In view of the potential environmental problem associated with stratospheric ozone depletion, there is a need for new materials possessing properties which make them useful substitutes for applications in which chlorofluorocarbons have been used and are environmentally safe. There is a limit to the number of single fluorinated hydrocarbon substances which can be candidates as environmentally safe materials. Mixtures of known fluorinated hydrocarbons, however, might be used if the desired combination or properties could be found in a given mixture. Simple mixtures, however, create problems in design and operation of refrigeration and other equipment because of component segregation in both the vapor and liquid phases. To avoid component segregation problems, it is particularly desirable to discover new substantially constant boiling fluorocarbon blends. Such blends should not suffer from component segregation problems. Unfortunately, it is not possible to predict the formation of constant boiling compositions, thus complicating the search for novel constant boiling compositions which possess the desired combination of properties. There is a need for substantially constant boiling compositions that have properties which make them particularly useful as refrigerants, aerosol propellants, heat transfer media, gaseous dielectrics, fire extmguishing agents, expansion agents for polyolefins and polyurethanes and as power cycle working fluids and that are potentially environmentally safe. SUMMARY OF THE INVENTION The present invention is directed to azeotropic compositions consisting essentially of about 5-45 weight percent, preferably about 4045 weight percent, pentafluoroethane, and 55-95 weight percent, preferably about 55-60 weight percent, 1,1,1-trifluoroethane, said composition boils at -16.9° C at about 51 psia. An especially preferred azeotrope consists essentially of 30 weight percent pentafluoroethane (CF3CHF2, boiling point = -48.5° C) and 70 weight percent 1,1,1-trifluoroethane (CF3CH3, boiling point = -47.6° C) , boiling at -16.9° C at about 51 psia. The novel compositions of the present invention exhibit lower vapor pressures than either of its two fluorocarbon constituents. The compositions described herein resist component segregation which would seriously diminish their usefulness in the contemplated applications. The substantially constant boiling azeotropic compositions are especially useful as refrigerants, heating applications, aerosol propellants, gaseous dielectrics, fire extmguishing agents, expansion agents for polyolefins and polyurethanes and as power cycle working fluids. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The fluorinated compounds which comprise these mixtures are identified in the industry as HFC-125 (pentafluoroethane) and HFC-143a (1,1,1- trifluoroethane) respectively, in nomenclature conventional to the halocarbon field. A phase study on various mixtures of pentafluoroethane and 1,1,1- trifluoroethane containing different amounts of the fluorocarbons indicate that at constant temperature an azeotrope is formed over the composition range studied. Further studies for the evaluation of substantially constant boiling compositions containing a wide range of proportions of the fluorocarbon components resulted in resistance to component fractionation of the mixture so that the compositions are substantially constant boiling at constant temperature. The insignificantly small change in vapor pressure at constant temperature illustrates that the amount of separation and loss of one fluorocarbon component in excess amount that would substantially change the boiling temperature of the mixture does not occur, which makes the compositions suitable for the contemplated uses, especially as a refrigerant. In addition, studies have further indicated that the novel azeotropic compositions of the present invention exhibit dew and bubble points with small pressure differentials. As is well known in the art, the difference between dew point and bubble point pressures is an indication of the constant boiling or azeotropic behavior of mixtures. The pressure differentials demonstrated by the substantially constant boiling compositions of the present invention are very small when compared with those of several known nonazeotropic, binary compositions. As is well recognized in this field of technology, there is a range of compositions which contain the same components as the true azeotrope, which not only will exhibit substantially equivalent properties as the true azeotrope for refrigerant and other applications but which will also exhibit substantially equivalent properties to the true azeotropic compositions in terms of constant boiling characteristics or tendency not to segregate or fractionate on boiling at other temperatures and pressures. Additives that are frequently incorporated in fluorocarbon compositions that can be added to the present compositions include lubricants, corrosion inhibitors, stabilizers and dyes. In addition to refrigeration applications, the novel substantially constant boiling azeotropic compositions of this invention are also useful as aerosol propellants, heat transfer media, gaseous dielectrics, fire extinguishing agents, expansion agents for polyolefins and polyurethanes and as power cycle working fluids. The fluorocarbon compositions described herein can be used to produce refrigeration by condensing the constant boiling azeotropic compositions and thereafter evaporating the compositions, e.g., condensate, in the vicinity of a body to be cooled. Further, these fluorocarbon compositions described herein can also be used to produce heat by condensing the constant boiling azeotropic compositions in the vicinity of a body to be heated and thereafter evaporating the compositions. The use of substantially constant boiling azeotropic compositions of this invention eliminates the problem of component fractionation and handling in system operations because fluorocarbon compositions behave substantially as a single substance. The fluorocarbon compositions of the present invention have zero ozone depletion potentials compared with Refrigerant 502, which has a 0.25 ozone depletion potential. The following Examples further illustrate the invention wherein parts and percentages are by weight unless otherwise indicated. EXAMPLE 1 A phase study was made on pentafluoroethane and 1,1,1- trifluoroethane wherein the composition was varied and the vapor pressures measured at a constant temperature of -16.9° C. An azeotropic composition was obtained, as evidenced by the minimum vapor pressure observed, and was identified as follows: TABLE 1 Pentafluoroethane = 30.5 _+ 5 weight percent 1,1,1-Trifluoroethane = 69.5.+ 5 weight percent Vapor pressure = 51.1 psia at -16.9° C EXAMPLE 2 Mixtures of from 5-45 weight percent pentafluoroethane (HFC- 125) and 55-95 weight percent 1,1,1-trifluoroethane are prepared and the vapor pressure at -16.9° C and 30° C is measured. The pressures generated by the compositions are given below in Table 2. The novel azeotropic compositions of the instant invention constituting a rather broad range of compositions and exhibit dew and bubble points with virtually no pressure differentials. As is well known in the art, the difference between dew point and bubble point pressures is an indication of the azeotrope-like behavior of mixtures. The pressure differentials demonstrated by the azeotropic mixtures of the instant invention are very small when compared with those of several known nonazeotropic, binary compositions, namely, (50+50) weight percent mixtures of pentafluoroethane (HFC-125) and 1,1,1,2- tetrafluoroethane (HFC- 134a) and chlorodifluoromethane (HCFC-22) and 1- chloro-l,l-difluoroethane (HCFC-142b), respectively, illustrated below. These data, which are shown in Table 3, confirm the azeotropic behavior of the compositions claimed in this invention. TABLE 3 A comparison of the refrigeration properties of the azeotropic composition of the invention with both Refrigerant 502 and pentafluoroethane (HFC- 125), respectively, is shown in Table 4. These data were generated on a one-ton basis, that is, on the removal of heat from a space at the rate of 12,000 BTU/hr. A liquid line/suction line heat exchanger was used, with a return gas temperature of 65° F ( 18.3° C). TABLE 4 Comparison of Refrigeration Performances Weight Percentages HFC-125 & HFC-143a Refrig. 502 HFC-125 (5+95) (30,5+69,5) (45+55) Evaporator Temp., °F -30.0 -30.0 -30.0 -30.0 -30.0 Evaporator Pressure, psia 23.10 27.6 27.28 27.01 26.73 Condenser Temp., °F 115.0 115.0 115.0 115.0 115.0 Condenser Pressure, psia 278.68 337.8 302.94 307.66 311.42 Coefficient of Performance 1.88 1.65 1.91 1.86 1.83 Net Refrigeration Effect. BTU/lb 47.23 37.12 59.52 53.56 50.55 Net refrigeration effect is intended to mean the change in enthalpy of the refrigerant in the evaporator, i.e., the heat removed by the refrigerant in the evaporator. Coefficient of performance (COP) is intended to mean the ratio of the net refrigeration effect to the compressor work. It is a measure of refrigerant energy efficiency. For a refrigeration cycle typified by the above conditions, the COP of the HFC-125/HFC-143a azeotrope in the amounts shown in Table 4 is similar to the COP of Refrigerant 502, the industry refrigerant standard, and better than that of pentafluoroethane (HFC-125). Having refrigeration characteristics similar to that of Refrigerant 502 is particularly desirable because the herein described azeotropic compositions can also be used, with Uttle or no modification to existing refrigeration equipment, which was designed originally for Refrigerant 502 use. Further, the present invention also provides compositions which surprisingly also have refrigeration characteristics substantially better than that of pentafluoroethane (HFC-125), the refrigerant currently recognized by the industry as the most plausible substitute for Refrigerant 502. The novel azeotropic mixtures have zero ozone depletion potentials compared with Refrigerant 502, which has a 0.25 ozone depletion potential.

Claims: CLAIMS: 1. Azeotropic compositions comprising 5-45 weight percent pentafluoroethane and 55-95 weight percent 1,1,1-trifluoroethane that have a boiling point of - 16.9° C at a vapor pressure of about 51 psia. 2. An azeotropic composition of Claim 1 comprising about 40-45 weight percent pentafluoroethane and about 55-60 weight percent 1,1,1- trifluoroethane. 3. An azeotropic composition of Claim 1 comprising about 30 weight percent pentafluoroethane and about 70 weight percent 1,1,1- trifluoroethane. 4. A process for producing refrigeration which comprises condensing the composition of Claims 1, 2 or 3 and thereafter evaporating the composition in the vicinity of a body to be cooled. 5. A process for producing heat which comprises condensing the composition of Claims 1, 2 or 3 in the vicinity of a body to be heated and thereafter evaporating the composition.

Inventors: BIVENS DONALD BERNARD, YOKOZEKI AKIMICHI, BIVENS, DONALD, BERNARD, YOKOZEKI, AKIMICHI
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1993
Main classification: C09K5
IPC codes: A62D1, C07C19, C08J9, C09K3, C09K5