US 2641579 A
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Patented June 9, 1953 AZEOTROPIC REFRIGERAN T COMPOSITION O F MONOCHLORODIFLUORO M E T HANE AND CHLOROPENTAFLUOROETHAN E Anthony Francis Benning, Woodstown, N. J., as-
signor to E. I. du Pont de Nemours and Company, Wilmington, 'Del., a corporation of Dela- Ware No Drawing. Application March 2, 1951, Serial No. 213,674
This invention relates to refrigerants and more particularly to fluorine-containing compounds and mixtures thereof which are useful as refrigerants.
The mixed fluorine and chlorine derivatives of methane and ethane have attained widespread use in the field of refrigeration as a result of their chemical inertness, their low specific volumes and the. wide range of boiling points which is available in the various members of the series. Difiuorodichloromethane (B. P. 29.8 C.), fluorotrichloromethane (B. P. 233 0.), fluorodichloromethane (B. P. 8.9 C.) and tetrafiuorodichloroethane (B. P. 3.5 C.) are among the most commonly used compounds of this type. Another valuable member of the series is monochlorodifluoromethane, which boils at 40.8 C. and which makes it possible to attain lower temperatures than can be reached with the compounds mentioned above. Highly eificient apparatus designed to use this material is in common use.
When apparatus designed to employ a particular refrigerant has been installed, the need sometimes arises for greater refrigerating capacity. This may be obtained by the use of a refrigerant having a lower boiling point and consequently a higher vapor pressure at the temperature attained by the gas prior to its being compressed and liquefied. The capacity of any given refrigeration compressor is roughly proportional to the pressure of the gas at the suction side of the compressor. Since the compressor can handle a fixed volume of gas per unit of time, an increase in the suction pressure means an increase in the number of moles of gas put through the compressor in a given time, An increase in the number of moles means an in crease in the total amount of heat required to vaporize the liquid in the evaporator, and an increase in the amount of heat that is removed from the refrigerated space. In general, other factors such as variations in the latent heat of vaporization play a relatively minor part in determining the change in capacity of a given refrigerating apparatus which will result from the substitution of one refrigerant for another.
In a given apparatus, it is not possible to use a refrigerant having a boiling point too much lower than that for which the apparatus has been designed, as the power input becomes undesirably high and the compressor motor becomes overloaded.
In order to provide greater refrigerating capac- 2 Claims. (Cl. 252-67) 2 r ity for installations designed for the use of monochlorodifiuo-ro-methane,- it is therefore desirable to employ a gas which may be liquefied a few degrees below the boiling point of that material. In this general boiling range, propane andpropylen are the only pure compounds known having suitable properties and sufficient availability for extensive use sis-refrigerants. Propane boils at 42 C. and propylene at -48 C. However, each of these compounds is flammable, and presents an explosion hazard caseor leakage.
The use of azeotropic mixtures of pure-materials as refrigerants is disclosed in U. S. Patent No. 2,101,993 and elsewhere in the art. Such mixtures have the advantage over other'gas mixtures that the vapor composition of the azeotrope is the same as the liquid composition with which it is in equilibrium. With non-azeotropi'cmixlow-boiling compositions which are useful as refrigerating agents, and more particularly to provide an azeotropic mixture which is effective in giving greater refrigerating capacity with apparatus designed for use with monochlorodifiuoromethane.
I have discovered that mixtures of monochloro-- difiuoromethane and chloropentafluoroethane form an azeotrope boiling at approximately -45.6 C., in which about 63 mol percent is monochlorodifluoromethane. The mixture is a highly useful refrigerant suitable for replacement of monochlorodifluoromethane in refrigeration equipment when a lower temperature or greater capacity is desired. Its use results in 22% greater refrigerating capacity than is-obtained with monochlorodifiuoromethane, other conditions being the same. This mixture has the further advantage that only slight changes in the boiling point occur when the composition is varied over a considerable range on either side of the actual azeotropic composition. Mixtures containing between 50 and mol percent monochlorodifluoromethane all boil between about 45.2 and 45.6 C., so that there is little tendency for fractionation to take place with any of thesemixtures. They are all effective refrigerating agents.
The boiling points of mixtures of monochlorodifluoromethane and chloropentafluoroethane were determined experimentally with the following results:
M01 percent monochlorodifluoromethane It is apparent from these figures that a minimum-boiling azeotrope exists at approximately 63 mol percent monochlorodifiuoromethane and that the change in boiling point between the limits of 50 and '75 mol percent monochloro difiuoromethane is very small. The boiling point of mixtures containing 50 mol percent of each component will be seen to be approximately -45.2 C.
In preparing these mixtures, it is desirable that the components be at least 99% pure and that they contain no appreciable amount of impurities which are corrosive or which separate upon evaporation, so as to interfere with the efiiciency of refrigeration. No special mixing procedure need be followed, provided the proper relative amounts of the two components are used.
The compositions disclosed herein are chemically inert, non-inflammable and are essentially non-corrosive. They combine the valuable characteristics possessed generally by fluorochlorohydrocarbons with a low boiling .point which is of particular significance when low temperatures are to be attained or when extra capacity must a be obtained with existing refrigerating equipment.
These refrigerants may be used in domestic or commercial refrigerators and freezers, industrial cooling systems and air-conditioning systems, or in any other system in which cooling is effected by the evaporation and expansion of liquid refrigerant. In such systems, the expanded gas is compressed and condensed to a liquid, and is recycled to the expansion device. Various specific types of refrigerating units for which the compositions here disclosed are of value are described in Refrigeration Fundamentals. 6th edition, 1949 (American Society of Refrigerating Engineers).
Iclaim: v 1. A 1ow-boiling refrigerant composition whic consists of a mixture of monochlorodifluoromethane and chloropentafluoroethane in which the mol percent of monochlorodifluoromethane 2. A low-boiling refrigerant composition consisting of a mixture of monochlorodifluoromethane and chloropentafiuoroethane, in which the mol percent of monochlorodifluoromethane is between and 75.
ANTHONY FRANCIS BENNING.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,479,259 Reed et a1. Aug. 16, 1949 2,511,993 Reed June 20, 1950 OTHER REFERENCES Kinetic Technical Bulletin-B2 Freon Compounds-Kin'etic Chemicals, Inc, Wilmington, De1.-l95011 page publication.