Ternary refrigerant compositions containing fluorinated ethers as replacements for R-22

Refrigerant compositions include mixtures of at least three different components, including a fluorinated ether with at least one of a second fluorinated ether, an ether and a fluorinated hydrocarbon. Also, methods for cooling a body include compressing such a refrigerant composition and bringing the body into heat transfer relation to it. The disclosed refrigerant compounds have refrigerant-significant properties similar to those of R-22, and they can be employed in place of or as drop-in substitutes in refrigeration apparatus designed for R-22 application.

BACKGROUND

1. Field of the Invention

This invention relates to refrigerants and, particularly, to mixtures suitable for use as substitutes for hydrochlorofluorocarbons (HCFCs) and chlorofluorocarbons (CFCs) in refrigeration. In particular the ternary compositions include components selected from fluorinated ethers, ethers and fluorinated hydrocarbons.

2. Description of Related Art

In recent years it has been suggested that release of certain hydrochlorofluorocarbons and chlorofluorocarbons may have adverse long-term effects on the earth's atmosphere. Particularly, these compounds are thought to undergo a ultraviolet radiation induced decomposition in the upper atmosphere, releasing chlorine atoms which are thought to react with ozone. The reaction of chlorine with ozone could reduce the extent of the protective stratospheric ozone layer. Depletion of the ozone layer could permit increased penetration of harmful ultraviolet radiation through the upper reaches of the atmosphere, with deleterious effects on the biosphere. Although this theory is not universally accepted, there has been a growing movement of international scope toward control of the production and use of certain CFCs and HCFCs.

Particularly, government regulation is forcing a phasing out of certain chlorine-containing refrigerants, and replacement of them with environmentally safer compounds. Accordingly, considerable effort has been directed toward finding alternatives for CFCs and HCFCs. Suitable refrigerant substitutes would be expected to have both a lower potential to damage the atmosphere and an acceptably high performance in the particular refrigeration systems in which they are intended as replacements for the conventional or first-generation CFC or HCFC refrigerants. For example, Sherwood U.S. Pat. No. 5,713,211 describes certain fluoroethers said to be useful in secondary loop refrigeration.

Thus far, no single compound has yet proven completely satisfactory as a replacement for any of the conventional CFC and HCFC refrigerants. For example, HCFC 134a (see below) has proven to be a satisfactory substitute refrigerant for CFC-12 in most but not all applications. Much of the developmental effort in this field has been directed toward finding suitable mixtures, and particularly azeotropic or azeotrope-like mixtures. For example, Lunger et al. U.S. Pat. No. 5,670,079 describes non-flammable azeotropic and azeotrope-like mixtures of a hydrocarbon and a fluorine-containing molecule, in which the atmospheric boiling points of the components differ by at least 20 C. Bivens et al. U.S. Pat. No. 4,810,403 describes refrigerant mixtures of three or more selected halocarbons, each one after the first having a successively higher boiling point, and having a temperature/pressure relation like that of dichlorodifluoro methane (CCl 2 F 2 , FC-12). Gage et al. U.S. Pat. No. 5,650,089 describes binary refrigerant mixtures, which may be azeotropic (or azeotrope-like) or zeotropic, in which the components are selected from certain hydrofluoroethers, hydrofluorocarbons, and hydrocarbons. Klug et al. U.S. Pat. No. 5,605,882 and U.S. Pat. No. 5,648,016 describe azeotropic and azeotrope-like mixtures of a fluoroether and a hydrofluorocarbon, said to be useful among other applications as refrigerants. Minor et al. U.S. Pat. No. 5,443,880 described binary refrigerant mixtures in which one of the components is a sulfur-containing compound. Pearson U.S. Pat. No. 5,108,637 describes refrigerants including ternary mixtures in nonflammable proportions , which may or may not be azeotropic. Shiflett U.S. Pat. No. 5,709,092 describes nonflammable near-azeotropic or essentially constant boiling mixtures of at least two components, and particularly ternary mixtures of certain fluorocarbons, said to be especially useful as supermarket case refrigerants. All the patents and other publications cited in this application are hereby incorporated herein in their entirety.

Chlorodifluoromethane (CHClF 2 , R-22) is one refrigerant for which a suitable substitute has been especially difficult to find. Refrigerant-significant parameters of a refrigerant mixture suitable for use as a R-22 substitute include: low boiling point (T b for R-22 is about 41 C.); high critical temperature (T c for R-22 is about 96 C.); critical mixing temperature well below the boiling point; and an acceptable flammability limit. Preferably the refrigerant is substantially non-corrosive to parts and fittings of the refrigeration apparatus which it contacts in use.

The situation remains that improved replacement refrigerants having optimum properties have not been reported. The present invention provides improved replacement mixtures.

SUMMARY OF THE INVENTION

We have discovered that certain combinations of three or more different compounds can provide refrigerant mixtures having refrigerant-significant properties that approximate those of R-22 and, accordingly, these mixtures are highly suitable as a drop-in substitute in R-22 refrigeration applications. The mixtures include at least one fluoroether, which may be a perfluoroether, and one or more of a second fluoroether, an ether and a fluorinated hydrocarbon. Preferred R-22 substitutes according to the invention are near-azeotropic, as these do not fractionate significantly over the range of temperature in use. Accordingly, in one general aspect the invention features a refrigerant composition that is a mixture of at least three different components, in which at least a first one of the components is a fluorinated ether and each of the second and the third components is a fluorinated ether, an ether and a fluorinated hydrocarbon. In some embodiments, each of at least three components is present in a proportion of at least 10 mole percent, and more usually one or more (most usually all) of at least three components is present in a proportion of at least 20 mole percent. It is understood that the total mol % of the ternary mixtures described herein must equal 100%.

In preferred embodiments the refrigerant composition is azeotropic or azeotrope-like. That is, it is a constant-boiling or substantially constant-boiling mixture of two or more substances that tends not to fractionate upon evaporation. Accordingly, the vapor produced by boiling or evaporation of the azeotropic or azeotrope-like mixture has the same or substantially the same composition as the liquid.

In another general aspect the invention features a method for cooling a body, by compressing a refrigeration composition according to the invention and bringing the body into heat transfer relation to it. The refrigeration compositions of the invention are effective drop-in substitutes for conventional CFC or HCFC refrigerants such as R-22, and can be employed in refrigeration apparatus designed for use with such conventional refrigerants, without significant retrofit or significant modifications. Some retrofit or modifications include, but are not limited to, compressor lubricant oils may need to be changed. Accordingly, in another general aspect the invention features a refrigeration system, including refrigeration apparatus configured and dimensioned for use with refrigerant R-22, charged with a refrigerant composition of the invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENT

Definitions

As used herein:

Fluorinated ether refers to the fluorinated ethers used in this art. Some are identified by a convention:

Term Fluorine - Containing 18S Trifluoromethyl pentafluoride R22 Chlorodifluoromethane 32 Difluormethine 116S Bis(trifluoromethlysulfide) 125 Pentafluoroethane 125E Pentafluorodimethyl ether 134a 1,1,1,2-Tetrafluoroethane 143a 1,1,1,-Trifluoroethane 152a 1,1-Difluoroethane 161 Fluoroethane 218E Perfluoromethyl ethyl ether Two-component mixtures having as one component a very highly fluorinated ether and as another component an HFC or ether with a low fluorine content may have boiling points and critical temperatures approaching those of R-22, but these are usually not miscible over the range of temperatures and pressures they encounter in use. We have discovered that admixture of a third component, particularly an ether, having a fluorine content between that of the first two components, can provide for improved miscibility and better refrigerant-significant characteristics. Usually, the highly fluorinated ether component has more fluorine atoms than hydrogen atoms per molecule, and may in some embodiments be perfluorinated; and a molecule of the component having the lowest fluorine content has fewer fluorine atoms than hydrogen atoms.

Particularly, for use as R-22 substitutes, preferred mixtures have a boiling point lower than 30 C., usually below about 32 C., still more usually below about 33 C. The boiling points are calculated from measured vapor pressure data using the following relation between Kelvin temperature (T) and the vapor pressure (P):

1n P A B 1n T C/T,

in which A, B, and C are empirically derived constants.

Particularly for use as R-22 substitutes, preferred mixtures have a critical temperature higher than about 70 C., still more usually higher than about 80 C., and most usually in the range about 85-100 C. The critical temperatures (T c ) of the mixtures are measured by slowly raising the temperature of the sample in a sealed tube until disappearance of the meniscus is observed. Alternatively or additionally, the critical temperature (T c ) can be estimated from the measured critical temperatures T ic , of the pure components and the component mole fractions X ic using the relation (for three components, i 1,2,3):

T c X 1 T 1c X 2 T 2c X 3 T 3c .

Preferred mixtures have a critical mixing temperature below the boiling point, usually at least about 5 C. below the boiling point.

The mixtures preferably are substantially non-flammable. Exceptions may include mixtures that contain both E-125 and R-161, and mixtures that contain both E-125 and R-152a. Generally, mixtures in which the fraction of C F and S-F bonds exceeds the fraction of C C and C H bonds are substantially non-flammable or have flammability limits that are acceptable for commercial units in the refrigeration industry.

The mixtures preferably are also substantially non-corrosive to fittings of standard R-22 refrigeration apparatus with which the refrigerant comes into contact in use.

Preferred mixtures are near-azeotropes; that is, they are characterized by showing less than about 2% separation at temperatures within the operational range.

The invention is now described in further detail.

Each of the components employed in the mixtures according to the invention is known, and either is commercially available in the desired purity or can be synthesized to the desired purity using published methods of synthesis. The patent literature in the refrigerant arts describes methods for synthesizing the various components, or refers to methods published elsewhere.

Particularly, where certain of the components may not be readily available commercially, the following methods are suggested.

The components may be combined by any of a variety of conventional methods to yield a mixture having the desired proportions.

A refrigeration system may be charged with a refrigerant mixture according to the invention by conventional means. Because the mixtures are effective as drop-in substitutes or replacements for R-22, they may be used to charge any refrigeration apparatus designed for use with R-22 refrigerant without retrofitting or mechanical adaptation.

EXAMPLES

Ternary Mixtures Including at Least Two Different Fluorinated Ethers

This example, referring to Table 1, shows exemplary ternary mixtures containing as a first component a fluorinated ether (particularly, perfluoromethyl ethyl ether (218E) or pentafluorodimethyl ether (125E)), and as a second component a different fluorinated ether, less fluorinated than the first (particularly, trifluoromethyl ethyl ether (143aE). A third component is a fluorinated hydrocarbon or a non-fluorinated ether.

Ternary Mixtures Including a Fluorinated Ether and at Least One Fluorinated Hydrocarbon

This example, referring to Table 2, shows exemplary ternary mixtures containing as a first component a fluorinated ether (particularly, perfluoromethyl ethyl ether (218E) or pentafluorodimethyl ether (125E)), and as a second component a fluorinated hydrocarbon. A third component can be a second fluorinated hydrocarbon, different from the first.

Ternary Mixtures Including a Fluorinated Ether and a Nonfluorinated Ether

This example, referring to Table 3, shows exemplary ternary mixtures containing as a first component a fluorinated ether (particularly, perfluoromethyl ethyl ether (218E)), and as a second component a nonfluorinated ether (particularly, dimethyl ether). A third component can be a fluorinated hydrocarbon.

Ternary Mixtures Including a Fluorinated Ether and a Fluorinated Sulfur-Containing Compound

This example, referring to Table 4, shows exemplary ternary mixtures containing as a first component a fluorinated ether (particularly, perfluoromethyl ethyl ether (218E)), and as a second component a fluorinated sulfur-containing compound (particularly, trifluoromethyl sulfur pentafluoride). A third component can be a fluorinated hydrocarbon.

While only a few embodiments of the invention have been shown and described herein, it will become apparent to those skilled in the art that various modifications and changes can be made in the improved replacement refrigerant compositions without departing from the spirit and scope of the present invention. All such modifications and changes coming within the scope of the appended claims are intended to be carried out thereby.