Azeotrope or azeotrope-like composition of trichlorotrifluoroethane and dichlorodifluoroethane

An azeotrope or azeotrope-like composition of 1,1,2-trichloro-1,2,2-trifluoroethane (FC-113) and 1,2-dichloro-1,1-difluoroethane (FC-132b), the azeotrope being useful in solvent cleaning applications.

BACKGROUND OF THE INVENTION 
Chlorocarbons and chlorofluorocarbons have obtained widespread use in 
recent years as specialty cleaning solvents for applications which include 
metal cleaning and degreasing and cleaning of printed circuit boards and 
instruments. Materials which are commonly used as solvents in these 
applications include 1,1,2-trichloro-1,2,2-trifluoroethane, 
trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane and an 
azeotrope of methylene chloride with 
1,1,2-trichloro-1,2,2-trifluoroethane. For certain cleaning purposes, the 
1,1,2-trichloro-1,2,2-trifluoroethane alone may have insufficient cleaning 
power while the chlorocarbon solvents may be too aggressive. The azeotrope 
of methylene chloride and 1,1,2-trichloro-1,2,2-trifluoroethane represents 
an ideal compromise as far as solvent power is concerned. However, 
increasing concerns over methylene chloride toxicity have made this 
solvent an unpopular choice. 
At the same time that chlorocarbon toxicity concerns are increasing, modern 
industrial cleaning problems are becoming more complex and varied, and the 
requirements for the cleaning solvents are more stringent. A solvent 
should be low boiling, nonflammable, of low toxicity, and should exhibit a 
high solvent power for the residues to be removed without being so strong 
that it attacks the substrate being cleaned. 
Desired boiling, flammability, and solvent power characteristics can often 
be obtained by using mixtures of solvents. However, mixtures are often 
unsatisfactory because they fractionate to an undesirable degree during 
use and recovery, making it difficult to reuse a solvent mixture with 
unchanged composition. 
On the other hand, mixtures which exhibit azeotropic or azeotrope-like 
characteristics are often used because they exhibit a minimum boiling 
point and do not fractionate upon boiling. This is desirable because in 
vapor degreasing and other cleaning operations, such as circuit board 
cleaning in which these solvents are also useful, redistilled material is 
usually used. Unless the solvent mixture exhibits a constant boiling 
point, i.e. is an azeotrope or is azeotrope-like, fractionation will occur 
and cause a change in the composition of the solvent mixture during use 
which could result in a mixture with less desirable properties. In the 
case of circuit board cleaning these less desirable properties could 
include lower solvency for rosin fluxes, reduced inertness toward 
electrical components and increased flammability. 
A number of fluorocarbon based azeotropic compositions have been discovered 
which have been tested and in some cases used as solvents for cleaning 
operations. For example, U.S. Pat. No. 2,999,815 discloses the azeotrope 
of 1,1,2-trichloro-1,2,2-trifluoroethane with acetone; U.S. Pat. No. 
3,903,009 discloses a ternary azeotrope of 
1,1,2-trichloro-1,2,2-trifluoroethane with nitromethane and ethanol; U.S. 
Pat. No. 3,573,213 discloses an azeotrope of 
1,1,2-trichloro-1,2,2-trifluoroethane with nitromethane; U.S. Pat. No. 
3,789,006 discloses the ternary azeotrope of 
1,1,2-trichloro-1,2,2-trifluoroethane with nitromethane and isopropanol; 
and U.S. Pat. No. 3,728,268 discloses the ternary azeotrope of 
1,1,2-trichloro-1,2,2-trifluoroethane with acetone and ethanol; and U.S. 
Pat. No. 2,999,817 discloses the binary azeotrope of 
1,1,2-trichloro-1,2,2-trifluoroethane and methylene chloride. 
Unfortunately, as recognized in the art, it is not possible to predict the 
formation of azeotropes and this obviously complicates the search for new 
azeotropic systems which have application in this field. Nevertheless, 
there is a constant effort in the art to discover new azeotropic or 
azeotrope-like systems which have desirable solvency characteristics and 
particularly a greater versatility of solvency power. 
SUMMARY OF THE INVENTION 
According to the present invention, an azeotrope or azeotrope-like 
composition has been discovered comprising an admixture of effective 
amounts of 1,1,2-trichloro-1,2,2-trifluoroethane and 
1,2-dichloro-1,1-difluoroethane, and more specifically, an admixture of 
about 45-60 wt. percent 1,1,2-trichloro-1,2,2-trifluoroethane and about 
55-40 wt. percent 1,2-dichloro-1,1-difluoroethane. 
The present invention provides a nonflammable azeotrope or azeotrope-like 
composition which is well suited for solvent cleaning applications. 
DETAILED DESCRIPTION OF THE INVENTION 
The compositions of the instant invention consist of mixtures of effective 
amounts of 1,1,2-trichloro-1,2,2-trifluoroethane (CCl.sub.2 FCClF.sub.2, 
boiling point 47.6.degree. C.) and 1,2-dichloro-1,1-difluoroethane 
(CClF.sub.2 CH.sub.2 Cl, b.p. 46.4.degree. C.). These two fluorinated 
materials are known as FC-113 and FC-132b, respectively, in the 
nomenclature conventional to the chlorofluorocarbon field. 
By azeotrope or azeotrope-like is meant constant boiling liquid admixtures 
of two or more substances which mixtures behave like a single substance in 
that the vapor produced by partial evaporation or distillation has the 
same composition as does the liquid, i.e., the admixtures distill without 
a substantial change in composition. Constant boiling compositions 
characterized as azeotropes or azeotrope-like exhibit either a maximum or 
minimum boiling point as compared with that of nonazeotropic mixtures of 
the same substances. 
By effective amount is meant the amount of each component of an admixture, 
which when combined will result in the formation of the azeotrope or 
azeotrope-like admixture of the instant invention. 
It is possible to fingerprint, in effect, a constant boiling admixture, 
which may appear under varying guises depending on the conditions chosen, 
by any of several criteria: 
The composition can be defined as an azeotrope of A and B, since the very 
term "azeotrope" is at once both definitive and limitative, requiring that 
effective amounts of A and B form this unique composition of matter which 
is a constant boiling admixture. 
It is well known by those who are skilled in the art that at differing 
pressures, the composition of a given azeotrope will vary, at least to 
some degree, and changes in distillation pressures also change, at least 
to some degree, the distillation temperatures. Thus, an azeotrope of A and 
B represents a unique type of relationship but with a variable composition 
depending upon temperature and/or pressure. Therefore, compositional 
ranges, rather than fixed compositions are often used to define 
azeotropes. 
Or, the composition can be defined as a particular weight percent 
relationship or mole percent relationship of A and B, while recognizing 
that such specific values point out only one particular such relationship 
and that in actuality a series of such relationships represented by A and 
B actually exist for a given azeotrope, varied by influence of 
distillative conditions of temperature and pressure. 
Or, recognizing that the azeotrope A and B does represent just such a 
series of relationships, the azeotropic series represented by A and B can 
be characterized by defining the composition as an azeotrope characterized 
by a boiling point at a given pressure, thus giving identifying 
characteristics without unduly limiting the scope of the invention by a 
specific numerical composition, which is limited by and is only as 
accurate as the analytical equipment available. 
Binary mixtures of 45-60 weight percent FC-113 and 55-40 weight percent 
FC-132b are characterized as an azeotrope or azeotrope-like in that 
mixtures within this range exhibit a substantially constant boiling point. 
Being substantially constant boiling, the mixtures do not tend to 
fractionate to any great extent upon evaporation. After evaporation, only 
a small difference exists between the composition of the vapor and the 
composition of the initial liquid phase. This difference is so small that 
the compositions of the vapor and liquid phases are considered 
substantially identical. Accordingly, any mixture within this range 
exhibits properties which are characteristic of a true binary azeotrope. 
The binary mixture consisting of about 50.5 weight percent FC-113 and about 
49.5 weight percent FC-132b with a boiling of about 44.2.degree. C. at 
substantially atmospheric pressure is the preferred azeotrope or 
azeotrope-like composition of this invention. 
The azeotropic mixtures of this invention can be used in a wide variety of 
solvent-cleaning applications, including vapor degreasing and metal 
cleaning applications and the removal of solder flux and other soils from 
printed circuit board assemblies. Vapor degeasers are generally used for 
cleaning flux and soils from printed circuit boards and metal parts. The 
object to be cleaned is usually passed through a sump of boiling solvent, 
which removes the majority of the soil; thereafter through a sump 
containing freshly distilled solvent at or near room temperature; and 
finally through solvent vapors over the boiling sump which provide a final 
rinse with clean pure solvent condensed on the object. The cleaning 
process can further comprise agitation to facilitate removal of the 
residues, including ultrasonic agitation of the cleaning agent or high 
pressure spray of the cleaning agent distillate. As an example, the 
azeotropic mixture of this invention can be used in cleaning processes 
such as is described in U.S. Pat. No. 3,881,949, which is incorporated 
herein by reference. 
The azeotrope of this invention has several advantages over the solvents 
heretofore employed. Trichloroethylene, tetrachloroethylene and 
1,1,1-trichloroethane are unstable and require stabilizers, whereas the 
azeotrope of this invention does not. In addition the azeotrope of this 
invention has a more favorable evaporation rate (is lower boiling) and is 
less aggressive toward plastics and elastomers. FC-132b is a stronger 
solvent than FC-113, which is often used in cleaning and degreasing 
operations. However, FC-132b alone may be too aggressive for some 
applications. Thus, the FC-113/FC132b azeotrope is particularly 
satisfactory for cleaning applications which require enhanced cleaning 
performance over FC-113 while maintaining the non-aggressive behavior of a 
mild solvent. 
The azeotrope permits easy recovery and reuse of the solvent from vapor 
defluxing systems because of its azeotropic nature. In addition, FC-113 
and FC-132b are nonflammable. Therefore, the azeotrope of this invention 
is nonflammable. 
The azeotrope of the instant invention can be prepared by any convenient 
method including mixing or combining the desired amounts of the 
components. A preferred method is to weigh the desired amounts of each 
component and thereafter combine them in an appropriate container.

EXAMPLE 1 
1,2-dichloro-1,1-difluoroethane (FC-132b) in a known amount was charged 
into a dry 2-neck round bottom flask fitted with a calibrated addition 
funnel and a reflux condenser having at its upper end a calcium sulfate 
drying tube and inside the condenser a calibrated thermometer suspended so 
as to place the bulb, wetted by condensate, in the vapor space. The 
FC-132b was heated to reflux by means of an electric heating mantle. From 
time to time 1,1,2-trichloro-1,2,2-trifluoroethane (FC-113) was added 
incrementally through the addition funnel. After each addition the system 
was allowed to equilibrate until the observed temperature of the vapor was 
constant. The barometric pressure was periodically recorded and the 
observed boiling points were corrected to 760 mm Hg pressure. 
The results of the above determinations are summarized in the following 
table. The composition of the mixture is represented as the weight percent 
of FC-113 in the FC-113/FC-132b mixture. The constancy of the boiling 
point over the composition range of about from 45-60 weight percent FC-113 
indicates the presence of the minimum boiling azeotrope. The minimum 
boiling point in a curve formed from these points indicates the true 
binary azeotrope at about 50.5 weight percent FC-113 and about 49.5 weight 
percent FC-132b. 
TABLE 
______________________________________ 
FC-113/FC-132b AZEOTROPE EXPERIMENTAL DATA 
Weight Percent FC-113 
in the 
FC-113/FC-132b Mixture 
Boiling Point .degree.C.* 
______________________________________ 
0.00 46.37 
10.00 45.56 
18.18 45.07 
25.00 44.76 
30.77 44.55 
35.71 44.39 
40.00 44.32 
43.75 44.27 
47.06 44.22 
49.43 44.21 
50.00 44.21 
50.55 44.20 
51.08 44.21 
51.61 44.21 
52.12 44.21 
52.63 44.21 
53.61 44.21 
54.54 44.22 
55.44 44.22 
56.31 44.23 
57.14 44.23 
59.09 44.24 
60.87 44.27 
64.00 44.33 
66.66 44.43 
100.00 47.60 
______________________________________ 
*Corrected to 760 mm Hg presure 
EXAMPLE 2 
Kauri-Butanol (KB) values are often used as a measure of solvent power. The 
KB value for the azeotrope of this invention (50.5 wt. percent FC-113 and 
49.5 wt. percent FC-132b), as measured by ASTM Method D1133-78, was 
determined to be 56.