Compositions – Vaporization – or expansion – refrigeration or heat or energy...
Reexamination Certificate
1999-09-30
2003-02-18
Einsmann, Margaret (Department: 1751)
Compositions
Vaporization, or expansion, refrigeration or heat or energy...
C252S068000
Reexamination Certificate
active
06521141
ABSTRACT:
The present invention relates to a refrigerant composition suitable for use in compression refrigeration.
Chlorofluorocarbons (CFCs), such as dichlorodifluoromethane (CFC-12), have traditionally been used as refrigerants for compression refrigeration systems. Refrigeration systems that use CFCs as refrigerants generally use mineral oils to lubricate the compressor. These lubricating mineral oils are also known as napthalenic oils. A lubricating mineral oil is typically a lube oil fraction having a viscosity index of from −300 to 140, which has been dewaxed, deasphalted and hydrogenated. The mineral oil may contain up to 15% by weight of an additive such as an antioxidant or a corrosion inhibitor. Typically, it has a kinematic viscosity at 40° C. of from 10 mm
2
/s to 220 mm
2
/s (10 cSt to 220 cSt).
In compression refrigeration systems it is desirable that all the lubricant should remain in the compressor to ensure that the compressor is adequately lubricated. In practice, however, an amount of lubricant is invariably aspirated into the surrounding pipework of the refrigeration cycle. If the lubricant is insoluble in the refrigerant, there is a danger that it will separate from the refrigerant and fail to return to the compressor. In this event, the compressor becomes inadequately lubricated. Refrigeration systems that use CFCs such as CFC-12 generally use mineral oil lubricants because such CFCs are soluble with the mineral oils throughout the entire range of refrigeration temperatures.
However, recent concern regarding depletion of the ozone layer by CFCs has led to the use of CFCs being restricted. CFC-12 has an ozone depletion potential of 0.9, where the ozone depletion potential of trichloromethane is defined to be 1. Alternative refrigerants are therefore required. Perfluorocarbons are not suitable as alternative refrigerants as they have a high global warming potential (GWP) and excessive atmospheric lifetimes. The GWP is the time-integrated commitment to climate forcing from the instantaneous release of 1 kg of refrigerant expressed relative to that from 1 kg of carbon dioxide, which is taken as having a GWP of 1.
1,1,1,2-tetrafluoroethane (R134a) is becoming widely used as an alternative to chlorofluorocarbon refrigerants. It has substantially no ozone depletion potential. It has a GWP, measured on the basis of a 100 year integrated time horizon, of about 1300. However, R134a has the disadvantage that it is substantially immiscible with the mineral oil lubricants used in existing refrigeration equipment. In other words, R134a cannot be used by itself in such equipment.
Various attempts have been made to find lubricants which can be used with fluorinated hydrocarbons such as R134a. Various polyolesters and polyalkylene glycols have been proposed for this purpose.
Unfortunately, however, these new lubricants are considerably more expensive than the conventional mineral oil lubricants. Also, they are often hydroscopic and absorb atmospheric moisture. Clearly, in order to minimise the changes necessary to the equipment or operating conditions when replacing CFCs in compression refrigeration systems with alternative refrigerants, it is desirable to be able to use the conventional mineral oils as used with the CFCs.
There is therefore a demand for a refrigerant which possesses the desirable properties of R134a but which can be used with the conventional mineral oil lubricants as used with the CFCs. Existing refrigerants which can be used with the mineral oil lubricants are invariably deficient in some other respect.
A novel refrigerant composition has now been devised, according to the present invention, which has substantially no ozone depletion potential, which is sufficiently compatible with the conventional mineral oil lubricants to be used with them and which has an operating performance equal to or superior to fluorinated hydrocarbons such as R134a and chlorofluorocarbons such as CFC-12.
The present invention provides a non-azeotropic refrigerant composition having a vapour pressure at −20° C. of from 70 to 190 kPa (0.7 to 1.9 bar), at +20° C. of from 510 to 630 kPa (5.1 to 6.3 bar) and at +60° C. of from 1620 to 1740 kPa (16.2 to 17.4 bar), which composition comprises:
(a) 1,1,2,2-tetrafluoroethane (R134), 1,1,1,2-tetrafluoroethane (R134a), difluoromethoxytrifluoromethane (E125) or a mixture of two or more thereof, in an amount of from 60 to 99% by weight, based on the weight of the composition;
(b) from 1 to 10% by weight, based on the weight of the composition, of an unsubstituted hydrocarbon of the formula C
n
H
m
in which n is at least 4 and m is at least 2n−2; and,
(c) up to 39% by weight, based on the weight of the composition, of a vapour pressure depressant,
Typically, a composition is “non-azeotropic” if, at any given pressure and temperature, the composition of the liquid and the composition of the vapour above the liquid are substantially not equal. Thus, any loss of vapour from a non-azeotropic composition will result in a composition change of the remaining liquid. In contrast, loss of vapour from an azeotrope does not result in a change of liquid composition.
Preferred non-azeotropic compositions are those in which, after about 50% of the composition is removed such as by evaporation or boiling off, the difference in the original composition and the composition remaining is more than about 2%, more preferably more than about 10%.
Typically, component (a) is present in an amount of from 70 to 95%, preferably from 80 to 90%, more preferably from 82 to 86%, by weight based on the composition.
Component (b) is an unsubstituted hydrocarbon of the formula C
n
H
m
, in which n is at least 4 and m is at least 2n−2. Typically, n is from 4 to 6, preferably 4 or 5. Typically, the unsubstituted hydrocarbon has no triple bonds. Preferably, the unsubstituted hydrocarbon is saturated except for one double bond. More preferably, the unsubstituted hydrocarbon is fully saturated.
Typically, the unsubstituted hydrocarbon is methylenecyclopropane, 1-butene, cis and trans-2-butene, butane, 2-methyl propane, cyclopentene, cyclopentane, 2-methyl-1-butene, 2-methyl-2-butene, 3-methyl-1-butene, 1-pentene, cis and trans-2-pentene, 2-methylbutane, pentane or a mixture of two or more thereof. Preferably, it is cyclobutane, more preferably n-butane (R600) or 2-methyl-propane (R600a).
Typically, the unsubstituted hydrocarbon is present in an amount of from 1 to 8%, preferably from 2 to 6%, more preferably from 2 to 5%, by weight based on the composition.
The unsubstituted hydrocarbon serves to improve the compatibility of the refrigerant composition of the invention with mineral oil lubricants. Unfortunately it increases the vapour pressure of the composition of the invention. It may also increase the flammability of the composition of the invention.
Accordingly, component (c) is required in order to reverse the increase in vapour-pressure caused by component (b). Component (c) is a vapour-pressure depressant, i.e. a compound capable of lowering the vapour pressure of the refrigerant composition.
Typically, the vapour-pressure depressant is 1,1-difluoroethane, 1,1,1,2,2,3,3-heptafluoropropane, 1,1,1,2,3,3,3-heptafluoropropane, octafluorocyclobutane, 1,1,1,2,2-pentafluoropropane, 1,1,2,2,3-pentafluoropropane, trifluoromethoxymethane, trifluoromethoxypentafluoroethane, difluoromethoxypentafluoroethane, trifluoromethoxy-1,2,2,2-tetrafluoroethane, fluoromethoxytrifluoromethane, difluoromethoxymethane, pentafluoroethoxypentafluoroethane, difluoromethoxydifluoromethane, trifluoromethoxy-2,2,2-trifluoroethane, fluoromethoxymethane, difluoromethoxy-1,2,2,2-tetrafluoroethane, fluoromethoxyfluoromethane, difluoromethoxy-2,2,2-trifluoroethane, methoxy-2,2,2-trifluoroethane, methoxy-1,1,2,2-tetrafluoroethane or a mixture of two or more thereof. Preferably it is 1,1-difluoroethane (R152a), 1,1,1,2,2,3,3-heptafluoropropane (R227ca), 1,1,1,2,3,3,3-heptafluoropropane (R227ea), 1,1,1,2,2-pentafluoropropane (R245cb), octafluorocyclobutane (RC-318) or a mixture of t
Einsmann Margaret
Rhodia Limited
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