Compositions – Vaporization – or expansion – refrigeration or heat or energy...
Reexamination Certificate
1999-07-12
2002-08-06
Einsmann, Margaret (Department: 1751)
Compositions
Vaporization, or expansion, refrigeration or heat or energy...
C062S114000, C252S068000
Reexamination Certificate
active
06428720
ABSTRACT:
The present invention relates to refrigerant compositions, particularly for use as replacements in refrigeration equipment currently employing, or designed to employ, the refrigerants R12 and R22.
Refrigerant R12 (CCl
2
F
2
) has been a commonly used refrigerant especially in domestic refrigerators. However, R12 contains chlorine atoms and has been implicated in environmental damage to the ozone layer. As a result efforts have been made to replace R12 with a refrigerant formulation which does not involve the use of refrigerants such as R12 which contain chlorine atoms. Similar comments apply to R22 which is used principally for airconditioning systems.
Among alternatives, particular attention has been directed at R134a (C
2
H
2
F
4
; 1,1,1,2-tetrafluoroethane) along with pentafluoroethane (R125) (b.pt. −48.6° C.). Commercial formulations of these two refrigerants involve the use of a hydrocarbon, namely propane, propylene or isobutane. While these refrigerant formulations are generally effective as replacements for R12 and R22, nevertheless it has been found that their use is not entirely satisfactory.
Difficulty has arisen with the flammability of the fractionated composition, that is to say the vapour above the liquid composition possesses flammability problems. As a result these commercial formulations can produce flammable compositions under some leak scenario conditions. The flammability of these refrigerant compositions resides in their hydrocarbon content. One of the purposes of incorporating the hydrocarbon is so that the formulation is compatible with the lubricants ordinarily used in R12 and R22 refrigeration equipment. The specific hydrocarbons have been selected because they possess the correct boiling point in relation to that of the fluorocarbon.
It has now been found, surprisingly, according to the present invention, that if a hydrocarbon with at least 4 carbon atoms other than methyl propane (isobutane) is used instead of those previously advocated the flammability of the fractionated composition is greatly reduced. This result is very surprising as n-butane, for example, has a significantly higher boiling point (−0.5° C.) than, say, isobutane (−11.7° C.) and is accordingly less volatile. Indeed, the US NIST (National Institute of Standards & Technology) computer programs REFPREP and REFLEAK have predicted that a particularly preferred such n-butane-containing formulation would be flammable when it has been found not to be. Further, although there can be a considerable boiling point range between the lowest boiling point component and the hydrocarbon of the composition the temperature glide of the blend is relatively small. In a particular embodiment, although the boiling point range is 36.2° C., the temperature glide is only 3.9K at the boiling point of −34.6° C. at one atmosphere pressure. It is further surprising that such a formulation has a reduced flammability because n-butane, for example, has a larger range of flammability limits as compared with isobutane. Thus n-butane has a flammability range from 1.5 to 10.1% v/v whereas for isobutane it is only 1.7 to 9.7% v/v.
According to the present invention there is provided a refrigerant composition which comprises:
(a) R125, R218 (octafluoropropane; b.pt. −36.7° C.), trifluoromethoxy difluoromethane (b.pt. −34.6° C.) or hexafluoro-cyclopropane (b.pt. −31.5° C.), or a mixture of two or more thereof, in an amount from 5 to 60% by weight based on the weight of the composition
(b) R125, R134a, R134 (1,1,2,2-tetrafluoroethane), 1,1-difluoroethane (R152a; b.pt. −24.7° C. ), trifluoromethoxypentafluoroethane (b.pt. −23.3° C. ), 1,1,2,3,3,3-heptafluoropropane (R227ea; b.pt. −18.3° C.) or 1,1,1,2,2,3,3-heptafluoropropane (R227ca; b.pt. −16.3° C.), or a mixture of two or more thereof, in an amount from 30 to 94% by weight based on the weight of the composition and
(c) an unsubstituted hydrocarbon of the formula C
n
H
m
in which n is at least 4 and m is at least 2n−2, other than methyl propane, in an amount from 1 to 10% by weight based on the weight of the composition.
The present invention also provides a process for producing refrigeration which comprises condensing a composition of the present invention and thereafter evaporating the composition in the vicinity of a body to, be cooled. The invention also provides a refrigeration apparatus containing, as refrigerant, a composition of the present invention.
Component (c) will be present in an amount from 1 to 10%, especially 1 to 8%, preferably 2 to 6% and more preferably 2 to 5%, and in particular 3 to 4%, most preferably about 3.5%, by weight of the composition.
It will be appreciated that component (a) and component (b) can both be R125. In this situation the composition can, therefore, be binary and the amount of R125 will be from 90 to 99% by weight. In all other situations, the composition will be at least ternary.
Among the preferred compositions of the present invention are those which contain one or more of R125, R134a and R218. Thus component (a) preferably comprises R125 and/or R218 while component (b) preferably comprises R125 and/or R134a.
The presence of R218 (b.pt −36.7° C.) is particularly useful where the only other fluorocarbon is R134a. In such circumstances R218 is particularly present in an amount from 5 to 20% by weight, especially 5 to 15%, and more preferably 7 to 12% by weight of the composition.
Component (a) is present in an amount from 5 to 60% by weight, generally 5 to 50% by weight. If R125 does not form part of component (a) then the amount will typically be from 5 to 20%, especially 5 to 15% and preferably 7 to 12%, by weight. It will be appreciated that if the composition contains R125, the concentration of R125 can be split between components (a) and (b).
The concentration of component (b) is from 30 to 94% by weight, generally 50 to 90% and especially 75 to 90%, by weight.
Typically hydrocarbons which can be employed as component (c), and which may be saturated or unsaturated, possess 4 or 5 carbon atoms and include methylenecyclopropane, 1-butene, cis and trans-2-butene, butane, cyclobutane, cyclopentene, cyclopentane, 2-methyl-1-butene, 2-methyl-2-butene, 3-methyl-1-butene, 1-pentene, cis and trans-2-pentene, 2-methylbutane, pentane and mixtures of two or more thereof. The use of n-butane (R600) is particularly preferred.
Specific formulations which have been found to be effective are as follows:
% by weight
% by weight
(a)
(b)
R218
9
R125
46
46.5
R134a
88
50
50
n-butane
3
4
3.5
It has also been found that certain compositions with specific amounts of n-butane as component (c) have particularly advantageous properties. According to the present invention, there is also provided a refrigerant composition which comprises (generally in the liquid phase):
(a) pentafluoroethane, octafluoropropane, trifluoromethoxydifluoromethane or hexafluoro-cyclopropane, or a mixture of two or more thereof, in an amount of at least about 35% based on the weight of the composition,
(b) 1,1,1,2- or 1,1,2,2-tetrafluoroethane, 1,1-difluoroethane, trifluoromethoxypentafluoroethane, 1,1,1,2,3,3-heptafluoropropane or a mixture of two or more thereof, in an amount of at least about 30% by weight based on the weight of the composition and
(c) n-butane, in an amount from about 2.3 to about 4% by weight based on the weight of the composition.
Component (a) is present in an amount of at least 35% by weight based on the weight of the composition. In practice, the concentration will generally be at least 40% by weight although a general range is 35 to 65% by weight. A preferred range is 40 to 55% by weight, especially 45 to 52% by weight. Preferably, component (a) is R125.
Component (b) is present in the composition in an amount of at least 30% by weight based on the weight of the composition. Typically, the component is present in an amount from 35% to 60% by weight, preferably 45 to 60% and especially 47.5 to 55% by weight. Component (b) is preferably R134a.
Component (c) is n-butane.
Einsmann Margaret
Rhodia Limited
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