Compositions – Vaporization – or expansion – refrigeration or heat or energy...
Reexamination Certificate
2000-03-20
2004-08-31
Hardee, John R. (Department: 1751)
Compositions
Vaporization, or expansion, refrigeration or heat or energy...
Reexamination Certificate
active
06783691
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to azeotrope-like compositions consisting essentially of difluoromethane, pentafluoroethane, 1,1,1,2-tetrafluoroethane and a hydrocarbon selected from the group consisting of: n-butane; isobutane; n-butane and 2-methylbutane; n-butane and n-pentane; isobutane and 2-methylbutane; and isobutane and n-pentane.
BACKGROUND
In recent years it has been pointed out that certain kinds of fluorinated hydrocarbon refrigerants released into the atmosphere may adversely affect the stratospheric ozone layer. Although this proposition has not yet been completely established, there is a movement toward control of the use and the production of certain chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) under an international agreement. Accordingly, there is a demand for the development of refrigerants that have a lower ozone depletion potential than conventional CFC and HCFC-based refrigerants while still achieving acceptable performance in refrigeration applications. Hydrofluorocarbons (HFCs) are gaining acceptance as replacements for CFCs and HCFCs as HFCs contain no chlorine and, therefore, have zero ozone depletion potential.
Mineral oils and alkylbenzenes have been conventionally used as lubricants in CFC-based refrigeration systems. However, the lack of solubility of these lubricants in HFC-based refrigerants has precluded their use and necessitated development and use of alternative lubricants for HFC-based refrigeration systems, which utilize polyalkylene glycols (PAGs) and polyol esters (POEs). A lubricant change from mineral oil or alkyl benzene to POE or PAG lubricants (which increases expenses in the refrigeration indusrty) is required when the HFC mixtures are used to replace CFC-based refrigerants. While the PAGs and POEs are suitable lubricants for HFC-based refrigeration systems, they are extremely hygroscopic and can absorb several thousand ppm (parts per million) of water upon exposure to moist air. This absorbed moisture leads to problems in the refrigeration system, such as formation of acids which causes corrosion of the refrigeration system, and the formation of intractable sludges. Conversely, mineral oils and alkylbenzenes are much less hygroscopic and have low solubility, less than 100 ppm, for water. Additionally, PAG and POE lubricants are considerably more expensive than the hydrocarbon lubricants, typically on the order of three to six times more expensive. Consequently, there is a need and an opportunity to resolve this solubility problem so that the refrigeration industry may utilize mineral oil and alkylbenzene lubricants with HFC-based refrigerants.
In refrigeration apparatus, refrigerant may be lost during operation through leaks in shaft seals, hose connections, soldered joints and broken lines. In addition, the refrigerant may be released to the atmosphere during maintenance procedures on refrigeration equipment. If the refrigerant is not a pure component or an azeotropic or azeotrope-like composition, the refrigerant composition may change when leaked or discharged to the atmosphere from the refrigeration apparatus, which may cause the refrigerant remaining in the equipment to become flammable or to exhibit unacceptable refrigeration performance. Accordingly, it is desirable to use as a refrigerant a single fluorinated hydrocarbon or an azeotropic or azeotrope-like composition which fractionates to a negilgible degree upon leak from a refrigeration apparatus.
In refrigeration applications where the potential of fire or fire's toxic byproducts are a concern, it is desirable for refrigerant compositions to be nonflammable in both liquid and vapor phases, when charging fresh refrigerant to a system or after refrigerant has leaked from a system.
Accordingly, there is a need in the refrigeration industry for compositions that are non-ozone depleting, nonflammable, and essentially non-fractionating azeotrope-like compositions. Additionally, there is a need in the refrigeration industry for compositions that offer improved return of conventional-refrigeration lubricating oils from non-compressor to compressor zones in compression-refrigeration apparatus, as well as superior refrigeration performance.
SUMMARY
The compositions of the present invention satsify the aforementioned needs confronting the refrigeration industry. The present compositions are useful as refrigerants, and in particular as HCFC-22 alternatives. Unlike compositions containing propane and pentane, compositions of the present invention are non-flammable in both liquid and vapor phases—as intially formulated and during leakage. The present invention is directed to azeotrope-like compositions consisting essentially of from about 1 to about 19 weight percent difluoromethane (HFC-32), from about 25 to about 60 weight percent pentafluoroethane (HFC-125), from about 24 to about 60 weight percent 1,1,1,2-tetrafluoroethane (HFC-134a) and from about 0.5 to about 5 weight percent of a hydrocarbon, wherein said hydrocarbon is selected from the group consisting of: n-butane; isobutane; n-butane and 2-methylbutane; n-butane and n-pentane; isobutane and 2-methylbutane; and isobutane and n-pentane.
DETAILED DESCRIPTION
The azeotrope-like compositions of the present invention consist essentially of difluoromethane (HFC-32, CH
2
F
2
, normal boiling point of −51.7° C.), pentafluoroethane (HFC-125, CF
3
CHF
2
, normal boiling point of −48.5° C.), 1,1,1,2-tetrafluoroethane (HFC-134a, CF
3
CHF
2
, normal boiling point of −26.1° C.) and a hydrocarbon selected from the group consisting of: n-butane (CH
3
CH
2
CH
2
CH
3
, normal boiling point of −0.5° C.); isobutane (CH(CH
3
)
3
, normal boiling point of −11.8° C.); n-butane and 2-methylbutane (CH
3
CH
2
CH(CH
3
)
2
, normal boiling point of 27.9° C.); n-butane and n-pentane (CH
3
CH
2
CH
2
CH
2
CH
3
, normal boiling point of 35.9° C.); isobutane and 2-methylbutane; and isobutane and n-pentane.
The azeotrope-like compositions of the present invention consist essentially of from about 1 to about 19 weight percent difluoromethane, from about 25 to about 60 weight percent pentafluoroethane, from about 24 to about 60 weight percent 1,1,1,2-tetrafluoroethane and from about 0.5 to about 5 weight percent of a hydrocarbon, said hydrocarbon selected from the group consisting of: n-butane; isobutane; n-butane and 2-methylbutane; n-butane and n-pentane; isobutane and 2-methylbutane; and isobutane and n-pentane. The preferred azeotrope-like compositions of the present invention consist essentially of from about 1 to about 15 weight percent difluoromethane, from about 30 to about 50 weight percent pentafluoroethane, from about 30 to about 50 weight percent 1,1,1,2-tetrafluoroethane and from about 1 to about 4 weight percent of the aforementioned hydrocarbons. The most preferred azeotrope-like compositions of the present invention consist essentially of 1-9 weight percent difluoromethane (HFC-32), 30-50 weight percent pentafluoroethane (HFC-125), 30-50 weight percent 1,1,1,2-tetrafluoroethane (HFC-134a) and 1-4 weight percent of the aforementioned hydrocarbons.
As previously stated, in refrigeration apparatus, refrigerant may be lost during operation through leaks in shaft seals, hose connections, soldered joints and broken lines. Additionally, the refrigerant may be released to the atmosphere during maintenance procedures on refrigeration equipment. If the refrigerant is not a pure component or an azeotropic or azeotrope-like composition, the refrigerant composition may change when leaked or discharged to the atmosphere from the refrigeration apparatus, which may cause the refrigerant remaining in the equipment to become flammable or to exhibit unacceptable refrigeration performance. Accordingly, it is desirable to use as a refrigerant a single fluorinated hydrocarbon or an azeotropic or azeotrope-like composition, such as the present invention, which fractionates to a negilgible degree upon leak from a refrigeration apparatus.
By azeotrope-like composition is meant a constant boili
Bivens Donald Bernard
Minor Barbara Haviland
Yokozeki Akimichi
E.I. du Pont de Nemours and Company
Edwards Mark A.
Hardee John R.
Sebree Chyrrea J.
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