Constant boiling mixtures of 1,2-difluoroethane and 1,1,2-trichloro-1,2,2-trifluoroethane

Constant boiling mixtures of 1,2-difluoroethane and 1,1,2-trichloro-1,2,2-trifluoroethane are useful as power fluids in low temperature Rankine cycles, and as refrigerants, aerosol propellants, expansion agents and solvents.

BACKGROUND OF THE INVENTION 
Methods whereby heat energy, and particularly waste heat energy, is 
transformed into useful mechanical energy by vapor power (Rankine) cycles 
is well known. The basic method comprises causing a suitable working or 
power fluid to pass in heat exchange relationship with a source of heat of 
sufficient intensity to vaporize the fluid; utilizing the kinetic energy 
of the expanding vapors to perform work by passing them through a turbine 
machine or other work producing device, condensing the vapor and pumping 
the condensed liquid back in heat exchange relationship with the heat 
source to complete the cycle. 
A variety of fluids have been tested in the past as power fluids for this 
type of application. Water or steam has been the most commercially 
utilized power fluid. However, the high boiling point, high critical 
pressure and low density of water or steam limit the power obtainable and 
result in a need for relatively large and bulky apparatus with these 
fluids. 
A number of organic liquids have been tested as power fluids (e.g. U.S. 
Pat. Nos. 2,301,404; 3,162,580; 3,234,738; 3,282,048; 3,516,248; and 
3,511,049), but there has not been found any single fluid suitable for use 
as a power fluid which possesses, to the optimum degree, all of the 
important properties of being thermally stable at elevated temperatures, 
non-corrosive to ordinary materials of construction and possession of a 
high Rankine cycle efficiency. 
In the development of Rankine cycle systems, the need exists for improved 
fluids possessing advantageous combinations of properties for Rankin cycle 
applications, particularly contributing a high Rankine cycle efficiency to 
the system. 
Since no single fluid has been found which is ideal for Rankine cycle 
applications, the art has turned to the preparation of blends or mixtures 
of fluids which give novel combinations of properties for Rankine cycle 
and other applications. 
Blends of 1,1-difluoroethane and monochloropentafluoroethane have been 
evaluated as refrigerants (World Refrigeration, February and March 1957), 
but such blends do not possess a desirable combination of properties for 
Rankine cycle applications. Blends of 1,1-dichloroethane and 
1,1,2-trichlorotrifluoroethane are also known (Canadian Patent No. 
832,341), but likewise do not possess a desirable combination of 
properties for Rankine cycle applications. 
Non-constant boiling blends are candidates for Rankine cycle applications, 
however, non-constant boiling mixtures suffer from the disadvantage that 
they fractionate during use and during reclamation thereby losing to a 
greater or lesser extend, one or more of the more volatile components, 
thereby changing the relative proportion of the components and hence, the 
properties of the mixtures. The changed properties may be less 
advantageous from the standpoint of Rankine cycle applications. 
The above described problem with non-constant boiling mixtures does not 
exist with constant boiling (or azeotropic) mixtures. Unfortunately, 
however, although azeotropic mixtures are advantageous for this reason, as 
evidenced by the disclosure in U.S. Pat. No. 3,085,065 to Kvalnes, a 
reliable basis has not been found for predicting the formaton of 
azeotropes, particularly among halocarbons. 
It is an object of this invention to provide a novel fluid mixture which 
has utility in Rankine cycle applications. 
It is another object of this invention to provide novel constant boiling 
compositions which have application in Rankine cycle systems. 
It is another object of the invention to provide constant boiling 
compositions which have high Rankine cycle efficiencies when used as 
working fluids in such systems. 
Other objects and advantages of the invention will be apparent from the 
following description. 
DESCRIPTION OF THE INVENTION 
In accordance with the present invention, we have discovered constant 
boiling mixtures consisting essentially of about 43 weight percent of 
1,2-trichlorotrifluoroethane at 760 mm. Hg. For the purpose of this 
discussion, by azeotropic or constant boiling is intended to mean also 
essentially azeotropic or essentially constant boiling. Included within 
the meaning of these terms are not only true azeotrope described above at 
760 mm Hg, but also other compositions containing the same components in 
different proportions which are true azeotropes at other pressures, as 
well as those equivalent compositions which are part of the same 
azeotropic system and are azeotrope-like in their properties. In other 
words, as will be well recognized in the art, there is a range of 
compositions containing the same components as the azeotrope, which, not 
only will exhibit essentially equivalent properties for Rankine cycle and 
other applications, but which will exhibit essentially equivalent 
properties to the true azeotropic composition in terms of its constant 
boiling characteristics or tendency not to fractionate upon boiling. 
In view of the constant boiling or essentially constant boiling 
characteristics of the novel compositions of the invention, these 
compositions can be recovered after use by distillation without change in 
composition. 
Methods of using the constant boiling compositions of the invention as 
working fluids in Rankine cycle applications will be obvious and well 
understood by those of ordinary skill in the art. Such methods essentially 
involve converting heat energy to mechanical energy by vaporizing the 
working fluid by passing the same in heat exchange relationship with a 
heat source and utilizing the kinetic energy of the resulting expanding 
vapors to perform work. Such methods, however, are not part of this 
invention. Detailed descriptions of the various Rankine cycle applications 
and methods of using working fluids in such applications are given in U.S. 
Pat. No. 3,282,048. Such applications, methods and techniques are 
applicable herein.

EXAMPLE I 
Equal molecular quantities of 1,2-difluoroethane (b.p. 29.6.degree. C./760 
mm) and 1,1,2-trichlorotrifluoroethane (b.p. 47.6.degree. C./760 mm) were 
charged to a still equipped with a fractionating column. This mixture was 
heated to reflux and then distilled. A fraction boiling at 24.9.degree. C. 
at 760 mm pressure was collected. Redistillation of this fraction showed 
no change in boiling point or composition. This fraction was analyzed by 
gas liquid chromatography and found to possess the following composition. 
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1,2-difluoroethane . . . 
43 weight percent 
1,1,2-trichloro- 
trifluoroethane . . . 
57 weight percent 
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EXAMPLE II 
In order to demonstrate the performance of the novel compositions of the 
invention in a typical low temperature Rankine cycle system, a comparison 
was made of the performance of the true azeotrope (43 weight percent 
1,2-difluoroethane and 57 weight percent 1,1,2-trichlorotrifluoroethane) 
with 1,1,2-trichlorotrifluoroethane. A comparison was not made with the 
1,2-difluoroethane component since this material is not as useful as a 
working fluid in Rankine cycle applications in view of its flammability. 
(1,2-Difluoroethane exhibits a flash point when measured by the Tag Open 
Cup Test-(ASTM D1310-72.)) The comparison is based on the Rankine cycle 
efficiency for these fluids. The data are based upon 100 percent turbine 
efficiency and although are not accurate on an absolute basis, are 
competent for the purpose of showing relative efficiency values. 
In the typical low temperature a Rankine cycle system chosen, a feed pump 
takes saturated liquid at low pressure (Condition 1) and pumps it to high 
pressure (Condition 1-A). At this point the fluid enters the boiler where 
heat is applied. This causes the fluid temperature to increase until 
boiling is achieved (Condition 2). Further heating in the boiler vaporizes 
the fluid until only saturated vapor remains (Condition 3). The vapors are 
then passed through an expansion engine where they expand at constant 
entropy or nearly so dependent on the engine efficiency. During the 
expansion process, useful work is done by the expansion engine and the 
vapors exit at a lower temperature and pressure (Condition 4). The vapors 
are then cooled further in a condenser where they again reach saturation 
conditions (Condition 5). Further cooling causes the vapors to condense to 
the saturated liquid condition (Condition 1), thus completing the cycle. 
Referring to the point conditions above, the enthalpy of the liquid or 
vapor for the working fluid can be defined as well as the Efficiency of 
the system. 
The Efficiency is given by: 
##EQU1## 
Table I compares the condition at various points of CCl.sub.2 FCClF.sub.2 
and the azeotrope for a cycle operating at a boiler temperature of 
300.degree. F and a condenser temperature of 120.degree. F. 
TABLE I 
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CC1.sub.2 FCC1F.sub.2 
Azeotrope 
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Pressure Boiler, psia 
173.5 369.1 
Pressure Condenser, psia 
15.36 33.55 
Enthalpy, Point 1, BUT/lb 
34.42 15.80 
Enthalpy, Point 3, " 
122.06 151.39 
Enthalpy, Point 4, " 
106.13 125.09 
Enthalpy, Point 5, " 
96.08 122.32 
Pump Work, BTU/lb 0.312 0.802 
Liquid Volume, Point 1, cu ft/lb 
0.0107 0.0129 
Efficiency .times. 100 
17.82 18.81 
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An analysis of Table I shows that the azeotrope would give a 5.6% 
improvement (18.81 - 17.82)/17.82 in Efficiency when operating over the 
temperature range described. In addition, the azeotrope has the advantage 
of less volume flow per unit of power and the ability to utilize lower 
condenser temperatures without having subatmospheric pressures. 
The thermodynamic data referred to in the above Table were computed. Such 
computation is based on measurement of the following: 
a. Critical Properties (Temperature, Pressure, Volume) 
b. Vapor Pressure 
c. Liquid Density 
d. Vapor Heat Capacity 
Representative data used in obtaining the thermodynamic properties of the 
azeotrope are as follows: 
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(a) Chemical Composition (wt %) 
1,1,2-trichloro-1,2,2-trifluoroethane (R-113) 
57 
1,2-difluoroethane (R-152) 43 
(b) Molecular Weight 104.6 
(c) Critical Temp. .degree. C 186.2 
(d) Critical Press. psia 682.4 
(e) Critical Density gm/cc 0.4517 
(f) Critical Volume cc/gm 2.2138 
(g) Liquid Density 
Temp. .degree. C Liquid Density (gm/cc) 
21.2 1.3000 
65.4 1.1995 
103.2 1.0992 
133.1 0.9989 
156.8 
156.8 
173.0 0.7989 
(h) Vapor Pressure 
Temp. .degree. C V.P. (psia) 
0.0 5.32 
50.0 34.76 
100.0 135.4 
150.0 376.6 
180.0 620.4 
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i. Vapor Heat Capacity 
The published data for R-152 and R-113 were used to obtain an equation for 
the vapor heat capacity of the R-152/R-113 azeotrope. 
From this data and using standard thermodynamic equations and techniques, 
thermodynamic tables were generated for the azeotrope. These tables relate 
the properties of enthalpy, entropy, pressure volume and temperature. 
The azeotrope exhibits no flash point when subjected to the Tag Open Cup 
Test (ASTM D1310-72). 
Additives, such as lubricants, corrosion inhibitors and others may be added 
to the novel compositions of the invention, for a variety of purposes 
provided they do not have an adverse influence on the compositions for 
their intended application. 
Some specific applications which may be mentioned as being exemplary for 
use of the subject power fluids include the utilization of energy from 
turbine exhaust gases. The recovery of heat in a variety of chemical 
synthesis plants and its conversion to mechanical energy to operate 
various auxiliary equipment. 
The novel compositions of the invention also possesses good heat transfer 
properties and other characteristics which make them useful as 
refrigerants. These novel fluids are especially suited for use in the 
split-cycle type refrigeration systems in which the fluid serves both as a 
refrigerant and as a power fluid, which in its power fluid capacity, 
drives the compressor and other components. 
In addition to Rankine cycle and refrigerant applications, the constant 
boiling composition of the invention are also useful as aerosol 
propellants, expansion agents such as for polyolefin and polyurethane 
foams, liquid dielectrics and as solvents for a variety of industrial 
applications.