Refrigeration – Processes – Employing diverse materials or particular material in...
Reexamination Certificate
2000-05-19
2003-04-15
Gupta, Yogendra N. (Department: 1751)
Refrigeration
Processes
Employing diverse materials or particular material in...
C062S114000, C252S067000, C252S068000
Reexamination Certificate
active
06546740
ABSTRACT:
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. The novel replacements for R-22 are ternary mixtures including components selected from hydrofluorocarbons, hydrofluoroethers and perfluoroorgano sulfur compounds.
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.
To date, no single compound has yet proven completely satisfactory as a replacement for any of the conventional CFC and HCFC refrigerants. For example, HCFC 134a 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 ethane (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 (CHClF2, 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.
SUMMARY OF THE INVENTION
We have discovered that certain combinations of three or more different compounds can provide refrigerant mixtures having 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 fluorinated sulfur-containing compound, and one or more of a fluorinated 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 sulfur-containing compound and each of the second and the third components is a fluorinated ether or a fluorinated hydrocarbon. In some embodiments, each of at least three components is present in a proportion 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 tht the total mol % of the ternary mixture described herein must equal 100%.
In some embodiments the fluorinated sulfur-containing compound is a fluorinated methyl sulfide. Particular fluorinated methyl sulfides include bis(trifluoromethyl) sulfide, CF
3
SCF
3
(116S); and trifluoromethylsulfur pentafluoride, CF
3
SF
5
(18S).
In some embodiments the fluorinated ether, where present, has the formula C
(n)
F
(m)
H
(2n+2−m)
O, where n=2 or 3, and 3≦m≦8. Particular fluorinated ethers include perfluoromethyl ethyl ether (trifluoromethyl pentafluoroethyl ether), CF
3
OCF
2
CF
3
(218E); pentafluorodimethyl ether, CF
3
OCF
2
H (125E); and trifluoromethyl methyl ether, CF
3
OCH
3
(143aE).
In some embodiments the fluorinated hydrocarbon, where present, has the formula C
(x)
F
(y)
H
(2x+2−y)
, where x=1 or 2, and 1≦y≦2x. Particular fluorinated hydrocarbons include 1,1,1,2-tetrafluoroethane, CF
3
CH
2
F (HFC-134a); 1,1,1-trifluoroethane, CF
3
CH
3
(HFC-143a); 1,1-difluoroethane, CH
3
CF
2
H (HFC-152a); fluoroethane, CH
3
CH
2
F (HFC-161); and difluoromethane, CH
2
F
2
(HFC-32).
Embodiments of the invention that may provide particularly useful performance in R-22 refrigerant applications include mixtures of, for example: (trifluoromethyl sulfur pentafluoride/218E/152a) in molar proportions, e.g., (0.10/0.45/0.45) or (0.254/0.373/0.373) or (0.3/0.3/0.4) or (0.20/0.25/0.55); (trifluoromethyl sulfur pentafluoride/134a/218E) in molar proportions, e.g., (0.10/0.45/0.45).
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 wit
Beyerlein Adolph L.
DesMarteau Darryl D.
Kul Ismail
Clemson University
Elhilo Eisa
Gupta Yogendra N.
Peters Howard M.
Peters, Verny, Jones & Schmitt, LLP
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