WO1993019117A1

WO1993019117A1 - Azeotrope-like compositions of 1,1,1,2,3,3,3-heptafluoropropane and 1,1-difluoroethane

Info

Publication number: WO1993019117A1
Application number: PCT/US1993/002829
Authority: WO
Inventors: Mark L. Robin
Original assignee: Great Lakes Chemical Corporation
Priority date: 1992-03-26
Filing date: 1993-03-26
Publication date: 1993-09-30
Also published as: AU3936293A

Abstract

Azeotrope-like compositions of 1,1,1,2,3,3,3-heptafluoropropane and 1,1-difluoroethane useful for heating and cooling applications, aerosol propellant applications and blowing agent applications.

Description

AZEOTROPE-LIKE COMPOSITIONS OF

1,1,1,2,3,3,3-HEPTAFLUOROPROPANE

AND 1,1-DIFLUOROETHANE

BACKGROUND OF THE INVENTION

Field of the Invention:

The present invention relates to azeotrope-like compositions of 1, 1, 1, 2, 3 ,3 , 3-heptafluoropropane and 1, 1-difluoroethane. These mixtures have no effect on stratospheric ozone and are useful as refrigerants for heating and cooling applications. These mixtures may also employed as aerosol propellants or as blowing agents for plastic foams.

Description of the Prior Art:

A number of chlorofluorocarbons (CFCs) have gained widespread use in refrigeration applications owing to their unique combination of physical and chemical properties. However, due to their implication in the destruction of stratospheric ozone, the production and use of CFCs is currently being severely restricted, and the use of these agents will be completely banned in the near future. This will require the replacement of these agents by refrigerant containing neither chlorine nor bromine and which have no effect on stratospheric ozone. One such zero ozone depleti compound which has been proposed is 1, 1-difluoroethane, (refrigerant R152a), which has been shown to provide 4 to 1 increases in efficiency compared to dichlorodifluoromethane (refrigerant R12), as discussed in Kuijpers, et al., in "CFCs: Time of Transition," ASHRAE, Atlanta, Ga, 1989, p. 175. A major drawback of this compound however is its high flammabilit . The use of azeotropic mixtures as refrigerants is known in the art, and is discussed for example in R.C. Downing, "Fluorocarbon Refrigerants Handbook," Prentice-Hall, 1988 an R.J. Dossat, "Principles of Ref igeration," 2nd edition, Wiley, 1981. Azeotropic or azeotrope-like compositions do not fractionate upon boiling or evaporation. This behavior is desirable when employing vapor compression equipment for refrigeration, since no fractionation will occur upon evaporation and condensation. Such fractionation can result in undesirable refrigerant distribution and also adversely affect the cooling or heating ability of the system.

Non-azeotropic refrigerant mixtures (NARMs) are known in the art, see, e.g., U.S. Patent 4,303,536, but have not foun widespread use. Since the NARMs fractionate during the refrigeration cycle, their use may require certain equipment changes.

The art is continually seeking new fluorocarbon based azeotrope-like mixtures which offer alternatives for refrigeration and heat pump applications and are efficient, nontoxic, non ozone depleting and nonflammable. As pointed out previously, although efficiency gains are observed employing 1, 1-difluoroethane, its high flammability is a serious liability to its practical use.

Computer-based models have substantiated that hydrofluorocarbons such as 1,1, 1,2,3,3,3-heptafluoropropane (HFC227ea) and 1, 1-difluoroethane (HFC152a) have no effect o stratospheric ozone, i.e., their ozone depletion potential (ODP) is zero.

The use of chlorofluorocarbons (CFCs) as blowing agents is well known in the art, but these materials are to be ultimately banned due to their role in the destruction of stratospheric ozone. It is also taught in the art that hydrochlorofluorocarbons (HCFCs) , for example 2,2-dichloro-l, 1,1-trifluoroethane (CF₃CHC1₂), are useful in foam blowing applications, see, e.g., I.R. Shankland, Int. J. Refriα.. 1_3_, 113 (1990). However, since the HCFCs are characterized by nonzero ozone depletion potentials, their use will also be restricted and likely banned in the future. It is also well known in the art to employ chlorofluorocarbons (CFCs) as aerosol propellants, see, e.g R.J. Hodson, in R.E. Banks, ec. , "Organofluorine Chemicals and their Industrial Applications," Horwood, 1979, p. 79. The ultimate ban of these materials due to their role in th destruction of the stratospheric ozone creates, however, a need for environmentally acceptable, nontoxic, nonflammable alternatives.

It is accordingly an object of this invention to provid novel azeotrope-like compositions based on 1,1,1,2,3,3,3-heptafluoropropane and 1,1-difluoroethane whi are nonflammable, nontoxic, chemically stable, and present adverse threat to stratospheric ozone. Another object of t invention is to provide novel environmentally acceptable refrigerants which are useful in cooling and heating applications. A further object of the invention is to provide environmentally acceptable, non-toxic, nonflammable aerosol propellants and foam blowing agents. Other objects of the invention will become apparent from the following description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the invention, novel azeotrope-li e compositions have been discovered comprising

1,1,1,2,3,3,3-heptafluoropropane and 1,1-difluoroethane. Th azeotrope-like compositions comprise from about 1 to about 5 weight percent 1,1,1,2,3,3,3-heptafluoropropane and from about 42 to 99 weight percent 1,1-difluoroethane. These compositions have a vapor pressure of about 78 psia (538 kPa at 70°F (21°C) . These compositions are azeotrope-like because they exhibit a maximum in the vapor pressure versus composition curve.

In a preferred embodiment of the invention, such azeotrope-like compositions comprise from about 5 to about 4 weight percent 1,1,1,2,3,3,3-heptafluoropropane and from about 95 to about 60 weight percent 1,1-difluoroethane. The compound 1,1,1,2,3,3,3-heptafluoropropane is known in the ar and has been shown to be an efficient fire suppression agent see, e.g., M. Robin, "Large Scale Testing of Halon Alternatives," 1991 International CFC and Halon Alternatives Conference, Baltimore, MD, December 3-5, 1991. Hence, non-flammable azeotrope-like mixtures are readily obtained b combining 1,1,1,2,3,3,3-heptafluoropropane with 1,1-difluoroethane.

A best estimate of the true azeotropic composition is about 28 weight percent 1, 1,1,2,3,3,3-heptafluoropropane and about 72 weight percent 1,1-difluoroethane, which has a vapo pressure of about 78 psia (538 kPa) at 70°F (21°C) . The mos preferred azeotrope-like compositions of the invention have vapor pressure of about 78 psia (538 kPa) at 70°F (21°C) . The term "azeotrope-like" is used herein for mixtures of the invention because in the claimed proportions the compositions of 1,1,1,2,3,3,3-heptafluoropropane and 1, 1-di luoroethane are constant boiling or essentially constant boiling. One method for determining whether a candidate mixture azeotrope-like is to determine whether the boiling point versus composition curve passes through an extremum, see, e.g., W. Swietoslawski , "Azeotropy and Polyazeotropy, " Pergamon, 1963, and J.M. Smith and H.C. Van Ness,

"Introduction to Chemical Engineering Thermodynamics," McGraw-Hill, 1987.

Alternatively, one can determine whether a candidate mixture is azeotrope-like by determining whether the vapor pressure versus composition curve passes through an extremu see, e.g., M. McLinden and G. Morrison, NBS Technical Note 1226, National Bureau of Standards, p. 96, 1986, Smith and Van Ness, op. QJA , and U.S. Patent 4,978,467. Azeotrope-like mixtures which possess a maximum in the vapo pressure versus composition curve will exhibit a minimum in the boiling point versus composition curve.

One of the characteristics of an azeotrope-like mixture is that there is a range of compositions containing the sam components in varying proportions which are azeotrope-like. It is well known to those skilled in the art that an azeotrope of two compounds represents a unique interaction but with a variable composition depending on the temperatur and/or pressure. For example, to those skilled in the art i is understood that the boiling point and composition of an azeotrope will vary with pressure.

Accordingly, another way to define an azeotrope-like mixture within the meaning of this invention is to state tha such mixtures exhibit vapor pressures within about +/- 5 psi (35 kPa) at 70°F (21°C) of the most preferred compositions disclosed herein (about 78 psia (538 kPa) at 70°F (21°C)). The inventive compositions are useful in a variety of applications. In one process embodiment of the invention, the azeotrope-like compositions of the invention may be used in the presence of a suitable lubricant if required, in a method for producing refrigeration which comprises condensin a refrigerant comprising the azeotropic-like compositions an thereafter evaporating the refrigerant in the vicinity of th body to be cooled. In another process embodiment of the invention, the azeotrope-like compositions of the invention may be used, in the presence of a suitable lubricant if required, in a method for producing heating which utilizes condensing a refrigerant comprising the azeotropic-like compositions in the vicinity of the body to be heated, and thereafter evaporating the refrigerant. As will also be readily appreciated by those skilled in the art, the azeotrope-like compositions of the invention are also useful in foam blowing and aerosol propellant applications.

It should be understood that the present compositions ma include additional, non-interfering components so as to form new azeotrope-like compositions. Any such compositions are considered to be within the scope of the present invention. The present invention is more fully illustrated by the following examples, which are to be understood as exemplary only, and non-limiting.

Example 1

This example shows that certain 1,1,1,2,3,3,3-heptafluoropropane (HFP) and 1, 1-difluoroethan (DFE) compositions exhibit essentially constant vapor pressures at a range of composition blends. The region of constant vapor pressure versus composition is used to define the constant-boiling or azeotrope-like range.

Vapor pressure measurements were performed by preparing mixtures of 1, 1, 1,2,3 ,3,3-heptafluoropropane and 1,1-difluoroethane in an approximately 300 cubic centimeter cylinder, equipped with a manual valve and pressure gauge (0-200 psig, accurate to +/- 0.5 psia). The vessel was submerged in a constant temperature bath controlled at +/- 0.05°C. The vapor pressure measurement was recorded onc thermal equilibrium was attained. This procedure was repeated for compositions having various weight percentages of the 1,1,1,2,3,3,3-heptafluoropropane and

1,1-difluoroethane. Table 1 summarizes the results of thes experiments.

Table I

Vapor Pressure at

Weight Percent 21.1°C 1,1,1,2,3,3,3-he tafluoropropane psia kPa

0.0 77 531 19.0 78 538

27.3 78 538 39.0 78 538 44.2 77 531

46.4 76 524 58.5 74 510

78.9 71 489

The data in Table I indicates that the vapor pressure remains essentially constant to within +/- 5 psia (34 kPa) from about 1 weight percent to about 58 weight percent 1,1,1,2,3,3,3-heptafluoropropane, and about 99 to about 42 weight percent 1,1-difluoroethane, i.e., this composition range is essentially constant boiling or azeotrope-like. Compositions ranging from about 5 to about 40 weight percen of the eptafluoropropane display particularly desired properties.

Example 2

This example shows that azeotrope-like blends of 1, 1, 1,2,3,3,3-heptafluoropropane and 1, 1-difluoroethane hav certain performance advantages when compared to R12 (dichlorodifluorornethane) .

The performance of a refrigerant at specific operating conditions can be derived from the thermodynamic properties of the refrigerants using standard ref igeration cycle analysis techniques, as reported for example in R.C. Downing "Fluorocarbon Refrigerant Handbook," ch. 3, Prentice-Hall (1988) . The coefficient of performance (COP) is a universally accepted measure useful in representing the relative thermodynamic efficiency of a refrigerant in a specific heating or cooling cycle, and is the ratio of useful refrigeration effect to the energy applied by the compressor in compressing the vapor. Refrigerant capacity represents the volumetric efficiency of the refrigerant.

Calculations of refrigerant performance have been carrie out employing the theoretical vapor compression model CYCLE7 available from the National Institute of Standards & Technology (NIST) for a medium temperature refrigeration cycle where the condenser temperature is typically 100°F and the evaporator temperature is typically -30° to 32°F. A pressure drop of 13.7 kPa across the condenser and evaporato is assumed, as well as an isentropic compressor efficiency o 55%. These conditions are typical of those found in normal applications. See, e.g., S. Fisher and J. Sand, "Thermodynamic Calculations for Mixtures of Environmentally Safe Refrigerants Using the Lee-Kesler-Plooker Equation of State," Preprints of 1990 USNC/IIR-Purdue Refrigeration Conference, p. 373. Calculations were performed for a 25/75 by weight blend of 1, 1, 1,2,3,3,3-heptafluoropropane and 1,1-difluoroethane as well as for 100 percent by weight 1, 1-difluoroethane and 100 percent by weight dichlorodifluorornethane (R12) . Table II lists the COPs and capacities, relative to that of R12. _g_

Table II

Thermodynamic Performance of 25/75 HFP/DFE Blend

Evaporator T = -30°C

Discharge

Evaporator T = -20°C

Discharge

COP Capacity Temperature (°C)

R12 1.000 1.00 110

DFE 1.109 0.97 127 HFP/DFE 1.061 0.93 115

Evaporator T = -10°C

Evaporator T - 0°C

Discharge

COPs and capacities are relative to R12 The data in Table II show that the 25/75 HFP/DFE blend provides a significant improvement in COP compared to that obtainable with R12. It provides essentially the same refrigeration capacity and also produces lower discharge temperatures from the compressor than HFC152a (DFE) , which leads to more reliable compressor operation. The performanc of the HFP/DFE blend is thus seen to offer superior performance compared to R12, and avoids the flammability problem associated with the use of DFE alone. The COP is determined for the various HFP/DFE formulations of Example 1 including for compositions having 5-40 weight percent of HFP and suitable COP'S are achieved.

Example 3

The foregoing formulations of Examples 1 and 2 are used as propellants and as blowing agents in conventional fashion and suitable results are obtained.

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

Claims

What is claimed is:

1. An azeotrope-like composition consisting essential of from about 5.0 to about 30.0 weight percent

1, 1, 1,2, 3.3 ,3-heptafluoropropane and from about 95.0 to ab 70.0 weight percent 1, 1-difluoroethane, said composition having a vapor pressure of between about 74 and 78 psi at about 21.1°C.

2. The composition of claim 1 and which has a vapor pressure of about 78 psia at 21.1°C.

3. The composition of claim 1 and which consists of 1, 1, 1,2 , 3, 3 , 3-heptafluoropropane and the 1, 1-difluoroethan

4. In a method of refrigeration comprising condensin and evaporating an azeotrope-like composition, the improvement comprising using an azeotrope-like composition comprising from about 5.0 to about 30.0 weight percent

1, 1, 1,2, 3 , 3,3-heptafluoropropane and from about 95.0 to ab 70.0 weight percent 1, 1-difluoroethane, said composition having a vapor pressure of between about 74 and 78 psi at about 21.1°C.

5. The improvement of claim 4 in which the azeotrope-like composition consists of the 1, 1, 1, 2 , 3 ,3 ,3-heptaf'luoropropane and the 1, 1-difluoroethan

6. A method of propelling a composition comprising propelling the composition with an azeotrope-like propella consisting essentially of from about 5.0 to about 30.0 weig percent 1, 1, 1, 2,3 ,3 ,3-hepta luoropropane and from about 95. to about weight percent 1, 1-difluoroethane, said compositio having a vapor pressure of between about 74 and 78 psi at about 21.1°C.

7. The method of claim 6 in which the azeotrope-like propellant consists of the 1,1,1,2, ,3,3-heptafluoropropane and the 1,1-difluoroethane.

8. A method of producing plastic foams from a materia which comprises foaming the material with an azeotrope-like composition comprising from about 5.0 to about 30.0 weight percent 1,1,1,2,3,3,3-heptafluoropropane and from about 95. to about 70.0 weight percent 1,1-difluoroethane, said composition having a vapor pressure of between about 74 and 78 psi at about 21.1°C.

9. The improvement of claim 8 in which the azeotrope-like composition consists of the

1,1,1,2,3,3,3-heptafluoropropane and the 1,1-difluoroel ane