FIELD OF THE INVENTION This invention relates to azeotropic and azeotrope-like mixtures of 1,1,2,2-tetrafluoroethane (HFC-134) and one of 1,1-difluoroethane (HFC-152a) , l-chloro-l,l-difluoroethane (HCFC-142b) , dimethyl ether (DME) , 1,1,1,2,3,3,3,-heptafluoropropane (HFC-227ea) , perfluorocyclobutane (FC-C318) , n-butane or isobutane and their use as refrigerants, aerosol propellants and blowing agents for polymer foams. The azeotropic and azeotrope-like compositions of 1,1,1,2- tetrafluoroethane and one of perfluorocyclobutane and 1,1,1,2,3,3,3-heptafluoropropane are also useful as fire extinguishants. As used herein, extinguishant means the active ingredient used to extinguish fires.

BACKGROUND OF THE INVENTION The mixtures of the present invention are useful as refrigerants, heat transfer media, gaseous dielectrics, foam expansion agents, aerosol propel¬ lants and power cycle working fluids. These mixtures are potentially environmentally safe substitutes for commercial refrigerants such as dichlorodifluorometh- ane (CFC-12) .

Closed-cell polyurethane foams are widely used for insulation purposes in building construction and in the manufacture of energy efficient electrical appliances. In the construction industry, polyure¬ thane (polyisocyanurate) board stock is used in roofing and siding for its insulation and load-carry¬ ing capabilities. Poured and sprayed polyurethane foams are also used in construction. Sprayed polyure-

thane foams are widely used for insulating large structures such as storage tanks, etc. Pour-in-plac polyurethane foams are used, for example, in appli¬ ances such as refrigerators and freezers, plus they are used in making refrigerated trucks and railcars. All of these various types of polyurethane foams require expansion agents (blowing agents) for their manufacture. Insulating foams depend on the us of halocarbon blowing agents, not only to foam the polymer, but primarily for their low vapor thermal conductivity, a very important characteristic for insulation value. Historically, polyurethane foams are made with trichlorofluoromethane (CFC-11) as the primary blowing agent.

A second important type of insulating foam is phenolic foam. These foams, which have very attractive flammability characteristics, are generall made with CFC-11 and CFC-113 blowing agents.

A third type of insulating foam is thermo¬ plastic foam, primarily polystyrene foam. Polyolefin foams (polyethylene and polypropylene) are widely use in packaging. These thermoplastic foams are generall made with CFC-12.

Many refrigeration applications, e.g. refrigerators, auto and window air conditioners, etc. presently use CFC-12 as the refrigerant. HFC-134 is fluorocarbon compound identified as a potential replacement for CFC-12, having properties near those of CFC-12, and being nonflammable with a zero ozone depletion potential. HFC-134 has a thermodynamic refrigeration coefficient of performance somewhat better than that of CFC-12, which may result in energ saving refrigeration applications when HFC-134 is substituted for CFC-12.

Many products designed for household, personal or industrial use are available as aerosol

products. Typical examples of such products and ones in which the propellant system of the present inven¬ tion can be used include personal products such as hair sprays, deodorants and colognes; household products such as waxes, polishes, pan sprays, room fresheners and household insecticides; industrial products such as cleaners, lubricants, and mold release agents; and automotive products such as cleaners and polishes. All such products utilize the pressure of a propellant gas or a mixture of propel¬ lant gases (i.e., a propellant gas system) to expel the active ingredients from the container. For this purpose, most aerosols employ liquified gases which vaporize and provide the pressure to propel the activ ingredients when the valve on the aerosol container i pressed open.

An important physical property associated with the dispensing of aerosol products is the vapor pressure of the propellant. Vapor pressure from the viewpoint of this invention is the pressure exerted when a liquified propellant gas is in equilibrium wit its vapor in a closed container, such as an aerosol can. Vapor pressure can be measured by connecting a pressure gauge to the valve on an aerosol can or gas cylinder containing the vapor/liquid mixture. A standard of measurement of vapor pressure in the U.S. aerosol industry is pounds per square inch gauge (psig) with the gas/liquid mixture at constant temper ature, most commonly at 70°F (21°C). The vapor pressures of liquified gases most widely employed as aerosol propellants will vary over the range of about 20 to 90 psig (239 to 722 kPa) at 70°F (21°C) . The propellant systems of the present invention have vapo pressures in this latter range.

In the early 1970s, concern began to be expressed that the stratospheric ozone layer (which provides protection against penetration of the earth atmosphere by ultraviolet radiation) was being depleted by chlorine atoms introduced to the atmo¬ sphere from the release of fully halogenated chloro- fluorocarbons. These chlorofluorocarbons are used a propellants in aerosols, as blowing agents for foams as refrigerants and as cleaning/drying solvent systems. Because of the great chemical stability of fully halogenated chlorofluorocarbons, according to the ozone depletion theory,these compounds do not decompose in the earth's atmosphere but reach the stratosphere where they slowly degrade, liberating chlorine atoms which in turn react with the ozone.

Concern reached such a level that in 1978 the U.S. Environmental Protection Agency (EPA) place a ban on nonessential uses of fully halogenated chlorofluorocarbons as aerosol propellants. This ba resulted in a dramatic shift in the U.S. away from chlorofluorocarbon propellants (except for exempted uses) to primarily hydrocarbon propellants. However, since the rest of the world did not join the U.S. in this aerosol ban, the net result has been to shift t uses of chlorofluorocarbons in aerosols out of the U.S., but not to permanently reduce the world-wide total chlorofluorocarbon production, as sought. In fact, in the last few years the total amount of chlorofluorocarbons manufactured worldwide has exceeded the level produced in 1978 (before the U.S. ban) .

During the period of 1978-1987, much research was conducted to study the ozone depletion theory. Because of the complexity of atmospheric chemistry, many questions relating to this theory

-5- remained unanswered. However, assuming the theory t be valid, the health risks which would result from depletion of the ozone layer are significant. This, coupled with the fact that worldwide production of chlorofluorocarbons has increased, has resulted in international efforts to reduce chlorofluorocarbon use. Particularly, in September, 1987, the United Nations through its Environment Programme (UNEP) issued a tentative proposal calling for a 50 percent reduction in worldwide production of fully halogenat chlorofluorocarbons by the year 1998. This proposal was ratified January 1, 1989 and became effective on July 1, 1989.

Because of this proposed reduction in availability of fully halogenated chlorofluorocarbon such as CFC-11, CFC-12 and CFC-113, alternative, mor environmentally acceptable, products are urgently needed.

As early as the 1970s with the initial emergence of the ozone depletion theory, it was know that the introduction of hydrogen into previously fully halogenated chlorofluorocarbons markedly reduc the chemical stability of these compounds. Hence, these now destabilized compounds would be expected t degrade in the atmosphere and not reach the strato¬ sphere and the ozone layer. The accompanying Table lists the ozone depletion potential for a variety of fully and partially halogenated halocarbons. Halo- carbon Global Warming Potential data (potential for reflecting infrared radiation (heat) back to earth a thereby raising the earth's surface temperature) are also shown.

TABLE I OZONE DEPLETION AND GREENHOUSE POTENTIALS

Blowing Agent CFC-11 (CFC1 ₃ ) CFC-12 (CF ₂ C1 ₂ ) HCFC-22 (CHF ₂ C1) HCFC-123 (CF ₃ CHC1 ₂ ) HCFC-124 (CF ₃ CHFC1) HFC-134a (CF !C—H2_F)

HFC-134 (CHF2_C ^C H ^H F ¹ 2_)'

HCFC-141b (CFC1 ₂ CH ₃ ) HCFC-142b (CF ₂ C1CH ₃ ) HFC-152a (CHF ₂ CH ₃ ) CFC-113 (CF ₂ C1-CFC1 ₂ ) FC-C318 (CF ₂ -CF ₂ ) (CF ₂ -CF ₂ ) HFC-227ea (CF ₃ CHFCF ₃ ) Not available

Halocarbons such as HFC-134, HFC-152a, HFC-227ea and FC-C318 have zero ozone depletion potential. Dimethyl ether, n-butane and isobutane, having no halogen content, are also zero ozone depleters. HCFC-142b has an ozone depletion potentia of 0.06.

Although 1,1,2,2-tetrafluoroethane has utility as a refrigerant, aerosol propellant or foam blowing agent, azeotropes offer the possibility of producing more economical nonfractionating systems with improved properties such as refrigeration performance, polymer and refrigerant oil solubility.

Unfortunately, as recognized in the art, it is not possible to predict the formation of azeo¬ tropes.

This fact obviously complicates the search for new azeotropes which have application in the field. Nevertheless, there is a constant effort in the art to discover new azeotropic compositions, whi have desirable characteristics.

SUMMARY OF THE INVENTION In accordance with the present invention, azeotropic or azeotrope-like mixtures have been discovered, which comprise effective amounts of 1,1,2,2-tetrafluoroethane (HFC-134) and one of 1,1-difluoroethane (HFC-152a) , 1-chloro-l,l- difluoroethane (HCFC-142b) , dimethyl ether (DME) , 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) , perfluorocyclobutane (FC-C318) , n-butane or isobutan

In accordance with the present invention, azeotropic or azeotrope-like mixtures have been discovered, which consist essentially of effective amounts of 1,1,2,2-tetrafluoroethane (HFC-134) and one of 1,1-difluoroethane (HFC-152a) , 1-chloro-l,1- difluoroethane (HCFC-142b) , dimethyl ether (DME) , 1,1,1,2,3,3,3-heptafluoropropane HFC-227ea, perfluorocyclobutane (FC-C318) , n-butane or isobutan

The azeotropes of HFC-134 and one of HCFC-142b, n-butane, HFC-227ea, isobutane and FC-C31 are minimum boiling azeotropes; thus, the vapor pressure is higher and the boiling point lower for t azeotropes than for the components. The azeotropes HFC-134 and one of DME and HFC-152a are maximum boiling azeotropes; thus, the vapor pressure is lowe and the boiling point higher for the azeotrope than for the components.

DETAILED DESCRIPTION OF THE INVENTION The novel azeotropic or azeotrope-like compositions of the invention were discovered during phase study wherein the compositions were varied and vapor pressures measured. By this procedure the following azeotropic compositions reported in Table were discovered:

* All compositions are + 2 wt. percent.

Atmospheric Boiling Points of Components, °C

HFC-134 -19.5 n-butane - 0.5

HFC-152a -25.0 Isobutane -11.7

HCFC-142b - 9.8 HFC-227ea -18.0

DME -24.6

FC-C318 - 6.1

For the purpose of this discussion, azeo¬ tropic, azeotropic-like or constant boiling is intended to mean also essentially azeotropic or essentially constant boiling. In other words, included within the meaning of these terms are not

only the true azeotrope described above, but also other compositions containing effective amount of t same components in somewhat different proportions, which are true azeotropes at other temperatures and pressures, as well as those equivalent compositions which are part of the same azeotropic system and ar azeotropic in their properties. As is well recogniz in this art, there is a range of compositions which contain the same components as the azeotrope, which not only will exhibit essentially equivalent proper¬ ties for refrigeration and other applications, but which will also exhibit essentially equivalent prope ties to the true azeotropic composition in terms of constant boiling characteristics or tendency not to segregate or fractionate on boiling.

It is possible to characterize, in effect, constant boiling admixture, which may appear under many guises, depending upon the conditions chosen, b any of several criteria:

* The composition can be defined as an azeotrope of A and B since the very term "azeotrope" is at once both definitive and limitative, and re¬ quires that effective amounts of A and B form this unique composition of matter, which is a constant boiling admixture at a given pressure.

* It is well known by those skilled in the art that at different pressures, the composition of given azeotrope will vary - at least to some degree and changes in pressure will also change - at least some degree - the boiling temperature. Thus, an azeotrope of A and B represents a unique type of relationship but with a variable composition which depends on temperature and/or pressure. Therefore, compositional ranges, rather than fixed compositions are often used to define azeotropes.

* The composition can be defined as a particular weight percent relationship or mole percen relationship of A and B while recognizing that such specific values point out only one particular such relationship and that in actuality, a series of such relationships, represented by A and B actually exist for a given azeotrope, varied by the influence of pressure.

* Azeotrope A and B can be characterized by defining the composition as an azeotrope characterize by a boiling point at a given pressure, thus giving identifying characteristics without unduly limiting the scope of the invention by a specific numerical composition, which is limited by and is only as accurate as the analytical equipment available.

It is recognized in the art that the difference between dew point temperature and bubble point temperature is an indication of the constant boiling or azeotrope-like behavior of mixtures. It has been unexpectedly found that compositions some distance away from the azeotrope compositions of this invention have differences in dew point/bubble point temperatures of less than or equal to one degree Celsius. The small temperatures differentials demonstrated by these compositions are less than values for azeotrope-like ternary mixture of HCFC-22, HFC-152a, and HCFC-124 described in U.S. Patent No. 4,810,403.

Therefore, included in this invention are the azeotrope-like compositions having dew point/bubble point differences of less than or equal to one degree Celsius reported in Table III. These data confirm the azeotrope-like behavior of the compositions claimed in this invention. The value for the ternary mixture of U.S. Patent No. 4,810.403 is shown for comparison.

* weight percent; 14.7 psia pressure,

The azeotropic and azeotrope-like compositions of the invention are useful as refrigerants, expansion agents and as aerosol propel¬ lants, among other applications. The azeotropic and azeotrope-like compositions of 1,1,1,2-tetrafluoro- ethane and one of perfluorocyclobutane and 1,1,1,2,3,3,3-heptafluoropropane are also useful as fire extinguishants.

Mixtures of HFC-134, HFC-227ea, and FC-C318 are nonflammable. The azeotropes of HFC-134 and HFC-152a or HCFC-142b are also nonflammable. Additionally, mixtures of HFC-134 and n-butane, isobutane and DME can be formulated such that they ar nonflammable. Therefore, the azeotropic compositions of HFC-134, n-butane, isobutane or DME are of significantly reduced flammability compared with n-butane, isobutane or DME alone.

Another aspect of the invention is a refri eration method which comprises condensing a refrige ant composition of the invention and thereafter evaporating it in the vicinity of a body to be coole Similarly, still another aspect of the invention is method for heating which comprises condensing the invention refrigerant in the vicinity of a body to b heated and thereafter evaporating the refrigerant.

In the heating and cooling applications, t nonflammable compositions are particularly useful.

These azeotropic and azeotrope-like compositions are useful as propellants for aerosol sprays, e.g., room fresheners. The azeotropes are particularly attractive as they do not separate or fractionate when used in aerosol packages equipped with vapor tap valves wherein the propellant is removed, at least partially, vapor phase.

The HFC-134/DME azeotropic and azeotrope-like compositions are excellent polymer blowing agents. The dimethyl ether component unexpectedly solubilizes the poorly soluble HFC-134 polyurethane, phenolic and polystyrene foam, resulti in excellent insulating foams. Once solubilized in the foam, the HFC-134 insulating gas does not diffus out of the foam. The compositions of this invention have vapor pressures and refrigeration energy efficiency values near that of CFC-12, hence are useful as refrigerants in refrigeration processes. They also show zero or low ozone depletion potential and compositions can be chosen such that they are nonflammable.

The binary refrigerant compositions of the invention are useful in compression cycle applicatio including air conditioner and heat pump systems for producing both cooling and heating. The new

refrigerant mixtures can be used in refrigeration applications as described in U.S. Patent No. 4,482,4 to Gray, which patent is incorporated herein by reference.

The HFC-134/dimethyl ether azeotrope of th invention has a vapor pressure at 70°F (21°C) of abo 45 psig (412 KPa) . This vapor pressure makes the azeotrope attractive and useful as an aerosol propel lant.

The HFC-134/dimethyl ether azeotrope has been determined to be soluble in polystyrene. Thus the azeotrope and, more particularly, the nonflammab mixtures of HFC-134 and dimethyl ether are potential excellent blowing agents for polystyrene.

Additionally, the HFC-134/dimethy3 ether azeotrope is soluble in polyurethane polyols; wherea FC-134 has quite poor solubility.

The language "consisting essentially of 1,1,2,2-tetrafluoroethane" is not intended to exclud the inclusion of minor amounts of other materials su as lubricants and stabilizers which do not signifi¬ cantly alter the azeotropic character of the azeo¬ tropic composition.

The compositions of the instant invention can be prepared by any convenient method including mixing or combining, by other suitable methods, the desired amounts of the components, using techniques well-known to the art.

Specific examples illustrating the inventi are given below. Unless otherwise stated therein, a percentages are by weight. It is to be understood that these examples are merely illustrative and in n way to be interpreted as limiting the scope of the invention.

EXAMPLE 1 A phase study was made on 1,1,2,2-tetra- fluoroethane (HFC-134) and HFC-152a, HCFC-142b, HFC-227ea, FC-C318, n-butane, isobutane and DME, respectively, wherein the compositions were varied the vapor pressures measured. The following azeotropic compositions reported in Table IV were defined:

* All compositions are + 2 wt. percent.

EXAMPLE 2 A determination was made of dew point and bubble point temperatures for the mixtures of the invention, shown in Table V. All have temperature differentials of less than or equal to one degree Celsius.

An evaluation of the refrigeration proper¬ ties of the mixtures of the invention versus dichlor difluoromethane (CFC-12) and 1,1,2,2-tetrafluoroetha (HFC-134) , respectively, are shown in following Tabl VI. The data were generated on a one ton basis, that is to say, on the removal of heat from a space at th rate of 12,000 Btu/hr (3516 watts). The data are based on the ideal refrigeration cycle.

TABLE VI COMPARISON OF REFRIGERATION PERFORMANCES

Weight Percentages

62% 75% 90% HFC-134 HFC-134 HFC-13

SubCOOl, °F 40 40 40 40 40

Coefficient of

Performance 2.42 2.50 2.36 2.58 2.

Displacement ft ³ /min/ton 8.1 10.4 10.3 12.4 12.

TABLE VI - (Cont'd) COMPARISON OF REFRIGERATION PERFORMANCES

Weight Percentage-

Displacement ft /mln/ton 10.3 10.9 10.5 10.7 12.9 12.0

Coefficient of Performance (COP) is a measure of refrigerant energy efficiency.

Additives such as lubricants, corrosion inhibitors, stabilizers, dyes and other appropriate materials may be added to the novel compositions of the invention for a variety of purposes provided the do not have an adverse influence on the composition, for their intended applications.

EXAMPLE 4 Aerosol room fresheners were prepared with the azeotropes of HFC-134 with HFC-l52a, HCFC-142b, DME, FC-C318, n-butane and isobutane. The formula¬ tions and vapor pressures are reported in Table VII.

TABLE VII AEROSOL ROOM FRESHENER FORMULATION Wt. %

Ingredient 1 2 3 4 5 6

Perfume 2.0 2.0 2.0 2.0 2.0 2.

Propellant* 98.0A 98.0B 98.0C 98.0D 98.0E 98.

Vapor Pressure 55 54 46 74.5 69 76 at 70 ^β F, psig

(21°C, kPa) (481) (474) (419) (615) (578) (626

* Propellants A - HFC-134/HFC-152a (97.4/2.6)

B - HFC-134/HCFC-142b (96.8/3.2) C - HFC-134/DME (74.4/25.3) D - HFC-134/FC-C318 (62.1/37.9) E - HFC-134/n-butane (82.5/17.5) F - HFC-134/isobutane (74.0/26.0)

EXAMPLE 5 The solubilities of the HFC-134 azeotropes were determined in a polyurethane polyol. The

azeotropes of HFC-134 with HFC-152a, HCFC-142b, DME, n-butane and isobutane were readily soluble at 30.0 wt. % in the polyol, as was HFC-134 itself. The solubility data are summarized in Table VIII.

TABLE VIII SOLUBILITY OF HFC-134/DIMETHYL ETHER AZEOTROPE IN POLYOL lowin A ent Wt.% in Pol ol Appearance

Soluble, single phas Soluble, single phas

Soluble, single phas

Soluble, single phas

Soluble, single phas

Soluble, single phas

* Stepanpol PS-2852 (Stepan Company) , an aromatic polyester polyol.

EXAMPLE 6 The solubility of the HFC-134 azeotropes i polystyrene was determined by combining a piece of polystyrene (about 2.5 cm long, 0.5 cm wide and 0.5 thick) with about 50 g. azeotrope. Only the HFC-134/DME (74.7/25.3) and the HFC-134/n-butane (82.5/17.5) azeotropes had any appreciable solubilit in polystyrene, softening and deforming the piece of polystyrene. The data are summarized in Table IX.

TABLE IX SOLUBILITY OF HFC-134 AZEOTROPES IN POLYSTYRENE

Blowing Agent Appearance of Polystyrene

HFC-134 Essentially no effect HFC-134/HFC-152a Essentially no effect

(97.4/2.6) HFC-134/HCFC-142b Essentially no effect

(96.8/3.2) HFC-134/FC-C318 Essentially no effect

(62.1/37.9) HFC-134/DME Polystyrene softened and

(74.7/25.3) deformed HFC-134/n-butane Polystyrene softened and

(82.5/17.5) deformed HFC-134/isobutane Essentially no effect

(74.0/26.0)

On removing the polystyrene from the azeotrope, expansion occurred from solubilized HFC-134.