WO1999025786A1

WO1999025786A1 - Hydrofluorocarbon refrigerants

Info

Publication number: WO1999025786A1
Application number: PCT/US1998/024771
Authority: WO
Inventors: Rajiv Ratna Singh; Ian Robert Shankland; Hang Thanh Pham; Gary Michael Knopeck
Original assignee: Alliedsignal Inc.
Priority date: 1997-11-18
Filing date: 1998-11-18
Publication date: 1999-05-27
Also published as: AU1594099A

Abstract

Mixtures of 1,1,1,2-tetrafluoroethane ('HFC-134a') or 1,1,2,2-tetrafluoroethane ('HFC-134') and 1,1,1,2,3,3,3-heptafluoropropane ('HFC-227ea') are provided. More specifically, the invention provides mixtures of HFC-134a or HFC-134 and HFC-227ea that are environmentally desirable replacements for chlorofluorocarbons and hydrochlorofluorocarbons as refrigerants, foam blowing agents, aerosol propellants, fire extinguishing agents, gaseous dielectrics, heat transfer media, metered dose inhalers, and the like.

Description

HYDROFLUOROCARBONREFRIGERANTS

Field of the Invention

This invention relates to mixtures of 1,1,1,2-tetrafluoroethane ("HFC- 134a") or 1,1,2,2-tetrafluoroethane ("HFC-134") and 1,1,1,2,3,3,3- heptafluoropropane ("HFC-227ea"). More specifically, the invention provides mixtures of HFC- 134a or HFC- 134 and HFC-227ea that are environmentally desirable replacements for chlorofiuorocarbons and hydrochlorofluorocarbons as refrigerants, foam blowing agents, aerosol propellants, fire extinguishing agents, gaseous dielectrics, heat transfer media, metered dose inhalers, and the like.

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.

While the primary purpose of refrigeration is to remove energy at low temperature, the primary purpose of a heat pump is to add energy at higher temperature. Heat pumps are considered reverse cycle systems because, for heating, the operation of the condenser is interchanged with that of the refrigeration evaporator.

The art is continually seeking new fluorocarbon based refrigerants and blowing agents that offer alternatives to chlorofiuorocarbons ("CFC's") and hydrochlorofluorocarbons ("HCFC's") currently in use. Of particular interest as alternatives are fluorocarbon based compositions that are considered to be environmentally safe substitutes Additionally, it is known that the use of either single component fluids or azeotropic mixtures, which mixtures do not fractionate on boiling and evaporating, is desirable. However, the identification of new, environmentally safe, azeotropic mixtures is complicated due to the fact that it is impossible to predict azeotrope formation.

Ideally, replacement refrigerant compositions possess those properties unique to the composition being replaced including chemical stability, low toxicity, non-flammability, and efficiency-in-use. The latter characteristic is important in refrigeration and air-conditioning applications 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 substitute would not require major engineering changes to conventional equipment currently used.

Similarly, CFC's have been used in metered dose inhalers in which the drug to be delivered to the lungs is suspended in a CFC, such as dichlorodifluoromethane ("CFC-12") or l,2-dichloro-l,l,2,2-tetrafluoroethane ("CFC-114"), and delivered as an aerosol. Ideally, the density of the drug or the surfactant used to suspend the drug should match the density of the aerosol propellant so that it is uniformly mixed with the propellant. Thus, it is advantageous for the propellant to have a density that may be varied so that it may match the densities of a wide variety of substances that are desired to be delivered by the inhalers.

Thus, the art is continually seeking new fluorocarbon based mixtures that offer alternatives, and are considered environmentally safe substitutes for CFC's and HCFC's. The present invention provides additional compounds and compositions that are suitable replacements. Description of the Invention

In accordance with the invention, it has been discovered that mixtures of

HFC- 134a or HFC- 134 and HFC-227ea are suitable replacements for CFC's and

HCFC's. More specifically it has been discovered that the mixtures of the invention meet the need for a nonflammable composition that has a low ozone depletion potential and is a negligible contributor to green-house global warming compared with currently used CFC's and HCFC's.

In one embodiment, the invention provides mixtures comprising, consisting essentially of, and consisting of HFC- 134a or HFC- 134 and HFC-227ea. For purposes of this invention, by mixtures is meant both nonazeotropic and azeotrope- like compositions.

In another embodiment, this invention provides azeotrope-like compositions comprising, consisting essentially of, and consisting of effective amounts of HFC-134a and HFC-227ea having a vapor pressure of about 62 to about 87 psia at about 21° C. By "effective amount" is meant an amount of each component that, when combined with the other component, results in the formation of an azeotrope or azeotrope-like mixture. The preferred, more preferred, and most preferred compositions are set forth in Table 1. The numerical values in Table 1 are to be understood to be prefaced by the term about.

Table 1

In still another embodiment of the invention provides azeotrope-like compositions comprising, consisting essentially of, and consisting of effective amounts of HFC- 134 and HFC-227ea having a vapor pressure of about 62 to about 71 psia at about 21° C. The preferred, more preferred, and most preferred compositions are set forth in Table 2. The numerical values in Table 2 are to be understood to be prefaced by the term about.

Table 2

For purposes of this invention, azeotrope-like compositions are compositions that behave like azeotropic mixtures. From fundamental principles, the thermodynamic state of a fluid is defined by pressure, temperature, liquid composition, and vapor composition. An azeotropic mixture is a system of two or more components in which the liquid composition and vapor composition are equal at the state pressure and temperature. In practice, this means that the components of an azeotropic mixture are constant boiling and cannot be separated during a phase change.

Azeotrope-like compositions behave like azeotropic mixtures, M , are constant boiling or essentially constant boiling. In other words, for azeotrope-like compositions, the composition of the vapor formed during boiling or evaporation is identical, or substantially identical, to the original liquid composition. Thus, with boiling or evaporation, the liquid composition changes, if at all, only to a minimal or negligible extent. This is to be contrasted with nonazeotrope-like compositions in which, during boiling or evaporation, the liquid composition changes to a substantial degree.

In yet another embodiment of the invention, non-azeotropic compositions comprising, consisting essentially of, and consisting of about 99 to about 10 weight percent HFC-134a or HFC-134 and about 1 to about 90 weight percent HFC-

227ea having a vapor pressure of from about 62 psia to about 70 psia at about 21 ° C are provided. In an embodiment of the invention, the mixtures and compositions of the invention may be used in a method for producing refrigeration that comprises, consists essentially of, and consists of condensing a refrigerant and thereafter evaporating the refrigerant in the vicinity of a body to be cooled. Alternatively, the compounds and mixtures of the invention may be used in a method for producing heating which comprises condensing a refrigerant in the vicinity of a body to be heated and thereafter evaporating the refrigerant.

In still another embodiment, the compounds and mixtures of the present invention may be used in a method for producing foam that comprises, consists essentially of, and consists of blending a heat plasticized resin with a volatile blowing agent comprising the fluids of the present invention and introducing the resin/volatile blowing agent blend into a zone of lower pressure to cause foaming.

In yet another embodiment the compounds and mixtures of the present invention may also be used in a method of dissolving contaminants or removing contaminants from the surface of a substrate that comprises, consists essentially of, and consists of the step of contacting the substrate with the compositions of the present invention. In another embodiment, the compounds and mixtures of the present invention may also be used as fire extinguishing agents.

In another embodiment, the mixtures and compositions of the invention are used as propellants in sprayable compositions, either alone or in combination with known propellants. The sprayable composition comprises, consists essentially of, and consists of a material to be sprayed and a propellant comprising, consisting essentially of, and consisting of a mixture or composition of the invention. Preferably, the sprayable composition is an aerosol. Suitable materials to be sprayed include, without limitation cosmetic materials such as deodorants, perfumes, hair sprays, cleansers, and polishing agents as well as medicinal materials such as anti-asthma and anti-halitosis medications. The mixtures and compositions of the present invention are known, commercially available materials. Preferably, the materials are used in sufficiently high purity so as to avoid the introduction of adverse influences upon the cooling or heating properties, constant-boiling properties, or blowing agent properties of the system. In the case of metered dose inhalers, the relevant current Good Manufacturing Process may be used for manufacturing these materials.

Additional components may be added to the compounds and compositions of this invention to tailor their properties according to the need. For example, in the art, propane may be added to refrigerant compositions to aid oil solubility and may be added to the fluids of the present invention. Nitromethane may also be added as a stabilizer. Similar materials may be added to the present compositions.

The present invention is more fully illustrated by the following, non-limiting examples.

Example 1 The vapor pressure of HFC-134a and HFC-227ea were measured at 0° C and 21.1° C in a 32 mL pressure vessel attached to a 0-300 psia transducer. The vessel was suspended in a temperature-controlled bath, the temperature of which was measured with a calibrated platinum resistance thermometer. The samples were degassed by a freeze, pump and thaw technique to eliminate errors caused by the presence of residual air. Table 3 shows the results.

Table 3

The negligible change in vapor pressure on addition of HFC-227 ea shows that compositions of HFC-134a and HFC-227ea are constant-boiling ot azeotrope-like. Example 2 The vapor pressure of HFC -134 and HFC-227ea were measured at 0 and

21.1° C in a 32 ml pressure vessel hooked to a 0-300 psia pressure transducer as in

Example 1. Table 4 shows the results.

Table 4

The negligible change in vapor pressure on addition of HFC-227ea to HFC -134 demonstrates that these compositions are constant-boiling or azeotrope-like. The small increase in pressure of the three mixture also indicates the existence of a true azeotrope in this system, between 8 and 37 weight percent HFC-134 in HFC-227 ea.

Example 3 This example shows that HFC-134a and HFC-227ea constant boiling compositions 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 as described, for example, in RC Downing, Fluorocarbon 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 evaporation or condensation of the refrigerant. In refrigeration engineering, this term expresses the ratio of useful refrigeration to the energy applied by the compressor in compressing the vapor. The capacity of a refrigerant represents the volumetric efficiency of the refrigerant. To a compressor engineer, this value expresses the capability of a compressor to pump quantities of heat for a given volumetric flow rate of refrigerant. In other words, given a specific compressor, a refrigerant with a higher capacity will deliver more cooling or heating power.

We have performed this type of calculation for a water chiller refrigeration cycle where the condenser temperature is typically 100° F and the evaporator temperature is typically 35° F. We have further assumed compression efficiency of 85 %, superheat of 10° F and a subcooling of 10° F. Such calculations were performed for various combinations of HFC-134a and HFC-227ea. Table 5 lists the COP and capacity of the various refrigerants.

Table 5

•Denotes that measurements are relative to HFC-134a.

It can be seen that without substantially reducing the energy efficiency or refrigeration capacity, the discharge temperature was substantially reduced. Lower discharge temperatures are associated with increased reliability and lifetime for refrigeration compressors.

Example 4 Large numbers of drugs are delivered through the use of metered dose inhalers, such as the bronchodilators fenoterol, ipratropium, ephedrine, and theophylline and the corticosteriods beclomethasone, budesonide, fluticasone, prenisolone, methylprednisolone, and hydrocortisone. The densities of these drugs vary, but generally are within the range of approximately 1.1 to 1.4 g cc. These drugs typically are immiscible in propellants used for their delivery. It is desirable that the drugs are mixed with a propellant that matches their density to avoid settling problems.

This example demonstrates that mixtures of HFC-134a and HFC-227ea can be formulated to provide a wide variety of densities thus providing useful propellants for drug delivery.

Table 6

Example 5

Thermoset foams are made using azeotrope-like mixtures of HFC-134a and HFC-227ea that are 5 weight percent HFC-227ea. 40 g of the azeotrope-like composition are charged to a 200 cc sealed vessel containing 3 g Dow styrene 685D. The vessel is placed in a 250° F oven overnight and the pressure released the next day. A good foam is obtained.

Claims

What is claimed is:

1. A composition comprising a mixture of 1 , 1 , 1 ,2-tetrafluoroethane or 1,1,2,2-tetrafluoroethane and 1,1,1,2,3,3,3-heptafluoropropane.

2. The composition of claim 1 wherein the mixture is an azeotrope-like composition comprising an effective amount of 1,1,1,2-tetrafluoroethane or 1,1,2,2-tetrafluoroethane and 1,1,1,2,3,3,3-heptafluoropropane.

3. The composition of claim 2 wherein the azeotrope-like composition comprises 1,1,1,2-tetrafluoroethane present in an amount of from about 99 to about 10 weight percent and 1,1,1,2,3,3,3-heptafluoropropane present in an amount from about 1 to about 90 weight percent the composition having a vapor pressure of about 62 to about 87 psia at about 21┬░ C.

4. The composition of claim 3 wherein the amount of 1 , 1 , 1 ,2- tetrafluoroethane is from about 95 to about 60 weight percent and the amount of 1,1,1,2,3,3,3-heptafluoropropane is from about 5 to about 40 weight percent.

5. The composition of claim 3 wherein the amount of 1,1,1,2- tetrafluoroethane is from about 95 to about 90 weight percent and the amount of 1,1,1,2,3,3,3-heptafluoropropane is from about 5 to about 10 weight percent.

6. The composition of claim 1 wherein the mixture is a nonazeotropic composition comprising 1,1,1 ,2-tetrafluoroethane or 1 , 1 ,2,2-tetrafluoroethane and

1,1,1,2,3,3,3-heptafluoropropane having a vapor pressure of from about 62 to about 70 psia at about 21┬░ C.

7. The composition of claim 6 wherein the nonazeotropic composition comprises 1,1,1,2-tetrafluoroethane present in an amount of from about 99 to about 10 weight percent and 1,1,1,2,3,3,3-heptafluoropropane present in an amount of from about 1 to about 90 weight percent.

8. The composition of claim 6 wherein the nonazeotropic composition comprises 1,1,2,2-tetrafluoroethane present in an amount of from about 99 to about 10 weight percent and 1,1,1,2,3,3,3-heptafluoropropane present in an amount of from about 1 to about 90 weight percent.

9. A method for producing refrigeration comprising condensing the composition of claims 1, 3, 4, or 5 and thereafter evaporating the refrigerant in the vicinity of a body to be cooled.

10. A method for producing heating comprising condensing the composition of claims 1, 3, 4, or 5 and thereafter evaporating the refrigerant.

11. A sprayable composition comprising a material to be- sprayed and a propellant comprising the composition of claims 1, 3, 4, 5, 7, or 8.

12. A sprayable composition according to claim 11 wherein the sprayable composition is an aerosol.

13. The composition of claim 12 wherein the material to be sprayed is a cosmetic material .

14. A sprayable composition according to claim 13 wherein the sprayable composition is an aerosol.

15. The composition of claim 12 wherein the material to be sprayed is a medicinal material.

16. A sprayable composition according to claim 15 wherein the sprayable composition is an aerosol.