In 1930 Midgley and Henne<28> discovered that various derivatives of methane and ethane, in which all—or almost all—of the hydrogen atoms were replaced by fluorine and chlorine atoms, had the desired properties for practically ideal refrigerants. They were nontoxic and
T A B L E X I I I
FLUOROCARBON T Y P E REFRIGERANT A N D PROPELLANTS OF M A J O R COMMERCIAL IMPORTANCE
M e t h a n e series Ethane series
nonflammable. They were first offered for sale in 1931 under the trade
mark, "Freon" halogenated hydrocarbons by the Kinetics Chemical Division of the E. I. duPont de Nemours and Company. Other companies in the United States have since introduced the same products using their own trade-names, i.e., "Genetron" (General Chemical Company),
"Isotron" (Pennsalt Manufacturing Company), and "Ucon" (Union Carbide Company). All the above companies have adopted the same code numbers for the same compounds. Those having the greatest commercial usage are listed in Table XIII.
A. PROPERTIES
There are many factors that must be taken into account when selecting a chemical for use as a refrigerant or an aerosol propellant. Besides boiling point, pressure, stability, toxicity, and flammability, such factors as mole
cular weight, density, compression ratio, heat value, temperature of
X = C I or F
F I G . 8. Properties of chlorofluoro derivatives of methane.
318 H . G . B R Y C E
compression, compressor displacement, design or type of compressor, etc., must also be considered.
A graphic presentation which was developed by Midgley and Henne(2 8'2 9> is quite useful in giving a better understanding of the pro
perties of a number of these fluorine-containing compounds, especially those which have been so widely accepted for use as refrigerants and also as "aerosol" propellants.
In the graph shown in Fig. 8 the rules of susbtitution will apply to typical groups having one carbon atom per molecule, or the methane series. It will be noted that when the fluorine content increases from that of CH2F2 (F-32) to CHF3 (F-23), the boiling point decreases, stability increases, flammability decreases, and toxicity decreases as indicated in the graph. Likewise, when the fluorine content increases still further to CF4 (F-14), the properties change to even lower boiling point, greater stability, and less toxic nature.
However, if the fluorine content remains constant and substitution is made for hydrogen by another halogen such as chlorine, the boiling point increases, stability and toxicity increase slightly, but flammability decreases. By again referring to Fig. 8, a similar change in properties will occur when the chlorine content is increased from CH2F2 (F-32) to CHCIF2 (F-22) and still further to CC12F2 (F-12).
In Table XIV are shown some of the important members of fully saturated fluorine-containing compounds in the methane series and ethane series. The general rules of substitution as reviewed for the methane derivatives will apply also to members of the ethane series; curves showing the changes in properties with halogen content have also been drawn<28>.
In the case of fluorine-containing compounds having two or more carbon atoms per molecule, fluorine substitutions can be made for hydrogen or chlorine on either of the two carbon atoms producing symmetrical or asymmetrical arrangement.
From a commercial viewpoint, primary interest is concerned with compounds in the methane and ethane series. In the United States F-12 accounts for almost half the production, with F - l l , F-22, F-114, and F-113 making up the bulk of the remaining production.
These compounds as refrigerants are adaptable for use in all com
pression types of refrigeration systems. The physical, chemical, and thermodynamic properties of quite a number of the fluorine-containing methane and ethane compounds have been carefully and fully studied and data published*1 8 8). However, a few of their outstanding properties will be reviewed.
The fluorine-containing chlorohydrocarbons are colorless, almost odorless, with boiling points varying over a wide temperature range.
TABLE XIV CHLORINE AND FLUORINE DERIVATIVES OF METHANE AND ETHANE Methane derivatives Code Formula Molecular weight Boiling point Code Formula Molecular weight Boiling point F-ll CCI3F 137.4 24°C F-21 CHCI2F 102.9 9°C F-12 CCI2F2 120.9 -30°C F-22 CHCIF2 86.5 -41°C F-13 CCIF3 104.5 -81°C F-23 CHF 3 70.0 -84°C F-14 CF 4 88 -128°C F-31 CH2CIF 68.5 -11°C F-32 CH2F2 52.0 -52°C F-41 CH 3F 34.0 -78°C Ethane derivatives F-lll CCI3CCI2F 220.3 137°C F-131c CHCI2CHCIF 151.4 103°C F-112 CCI2FCCI2F 203.8 93 °C F-132c CHCI2CHF2 135.0 60°C F-113 CCI2FCCIF2 187.4 48°C F-133c CHCIFCHF2 118.5 17°C F-114 CCIF2CCIF2 170.9 4.7°C F-134c CHF2CHF2 102.0 -23°C F-ll 5 CCIF2CF3 154.5 -38°C F-141a CH2CICHCIF 116.9 74°C F-116 CF 3CF 3 134.0 -78.4°C F-142a CH2CICHF2 100.5 35°C F-121 CHCI2CCI2F 185.8 117°C F-143a CH2FCHF2 84.0 5°C F-122 CHCI2CCIF2 169.5 71.7°C F-151a CH2CICH2F 82.5 35°C F-122b CHCIFCCIF2 152.5 28°C F-152 CH3CHF2 66.0 -25°C F-124a CHF2CCIF2 136.5 -10°C F-161 CH 3CH 2F 48.0 -37°C F-125 CHF2CF3 120.0 -48°C
320 H. G. BRYCE
Those that are of primary importance in the field of refrigeration as well as propellants are essentially nontoxic, noncorrosive, nonirritating, and nonflammable under normal conditions of usage. They are generally prepared by replacing chlorine or hydrogen with fluorine. Chemically they are inert and thermally stable up to temperatures far beyond con
ditions found in actual use as refrigerants or propellants.
B. REFRIGERATION CHARACTERISTICS
Pressures required to liquefy the refrigerant vapor affect the design of the system; refrigerating effect and specific volume of the refrigerant vapor determine the compressor displacement; and the heat of vaporiza
tion and specific volume of liquid refrigerant affect the quantity of re
frigerant to be circulated through the pressure regulating valve or other device. Table XV covers boiling point at one atmosphere, freezing point,
T A B L E X V
COMPARISON OF VARIOUS REFRIGERANTS*3 0*
Refrigerant Boiling Freezing Critical Critical point point temperature pressure
(°C) (°C) (°C) (psi,
critical temperature, and critical pressures of not only the fluorine-con
taining methane and ethane derivatives, but other commonly used refriger
ants.
The chlorofluoro derivatives of methane and ethane have relatively low heat values. This should not be considered a disadvantage since this merely means that a greater volume of liquid must be pumped through the system per unit time to produce the required amount of refrigeration.
From an engineering point of view, this turns out to be a decided advantage, especially for small tonnage units, since more accurate and reliable control of liquid flow is possible when larger flows of liquid are involved. The heat values for both liquid and vapor, as well as relative refrigerating effect of a number of common refrigerants, is shown in Table XVI.
T A B L E X V I
H E A T V A L U E S FOR L I Q U I D A N D V A P O R STATES FOR V A R I O U S REFRIGERANTS
Heat value ( B T U per lb) Refrigerating Refrigerant Vapor Liquid effect
( - 1 5 ° C ) (30°C)
CCIF2CCIF2 (F-114) 22.0 16.1"
CC13F(F-11) 3.6 24.0«
a U n i t s are inches of mercury below one atmosphere.
In Table XVII are given the operating pressures for a series of standard refrigerants based on standard ton conditions. Carbon dioxide has a much higher pressure than the others, with a consequent much higher horsepower requirement.
In Table XVI11 data is given on the explosive properties of refriger
ants as established by the Underwriters Laboratories<31>. All the flourine-containing refrigerants are nonflammable.
322 H. G. BRYCE
Table XIX contains data on the comparative toxic properties of various refrigerants <31).
These fluorine-containing halocarbons have characteristic physical and thermodynamic properties which make them readily adaptable for use in reciprocating, rotary, and centrifugal compressors, which vary in size
T A B L E X V I I I Refrigerant Duration of exposure to kill or injure
seriously
from fractional refrigeration tonnage to several thousand tons capacity.
They produce wide ranges of temperatures from room temperatures to low subzero temperatures. The particular choice depends upon size and type of installation and also the desired cooling capacity.
C. APPLICATIONS FOR SPECIFIC COMPOUNDS
F-12 (CCI2F2), having a boiling point of — 21.6°F and a pressure of 93.2 psig at 86°F, is used extensively as an aerosol propellant for such items as insecticides, insect repellants, deodorizers, hair dressings, and a host of other products. F-22 (CHCIF2), besides being used as a low temper
ature refrigerant, is also used as an intermediate in the production of polytetrafluoroethylene. F-113 (CCI2-FCCIF2) is used in heavy duty air conditioning units and is also useful as a specialty solvent and as an inter
mediate in the production of polychlorotrifluoroethylene.
Recently the compound, C-C4F8, octafluorocyclobutane<32>, has been introduced as a nontoxic material for use as an aerosol propellant in food applications such as whipped cream, salad dressings, pancake mixes, etc.
This material boils at — 6°C and has a vapor pressure of 40 psi absolute at 21 °C. Although the chlorine-containing compounds are relatively nontoxic,, their use has not been permitted in food applications since, as the data in Table XIX shows, they do have some toxic effects at relatively high levels. This use emphasizes again the fact that a compound containing only carbon and fluorine is essentially nontoxic; whereas the presence of chlorine or hydrogen atoms in the molecule introduces some degree of solubility in body fluids which are both aqueous or organic in nature.