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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to non-flammable mixtures of perchloroethylene and
monochlorotoluene. In particular, it relates to mixtures of about 25 to
about 85 wt % perchloroethylene with about 15 to about 75 wt %
monochlorotoluene.
The solvent 1,1,1-trichloroethane is used in a variety of industrial
applications because it is a good solvent for many organic compounds and
it lacks a flash point under normal conditions of use, thereby providing a
margin of fire safety to workers. While it is believed to be of low
toxicity and non-carcinogenic, it has recently been implicated in the
destruction of stratospheric ozone. As a result, its use will probably be
phased out over the next decade and it is likely to be banned entirely
early in the 21st century.
Industrial chemists and engineers are currently expending considerable
funds and manpower to find a solvent that can replace
1,1,1-trichloroethane. Such a solvent would have to retain
1,1,1-trichloroethane's desirable properties, such as the absence of a
flash point, the ability to dissolve a wide variety of organic compounds,
and low toxicity and carcinogenicity, but would not have a deleterious
effect on stratospheric ozone.
SUMMARY OF THE INVENTION
I have discovered that certain mixtures of perchloroethylene with
monochlorotoluene do not have a flash point (i.e., the mixture boils
before it ignites). This is surprising because mixtures of
perchloroethylene with other aliphatic and aromatic compounds do have a
flash point. Moreover, it is also surprising that the absence of a flash
point in a perchloroethylene-monochlorotoluene mixture occurs when the
perchloroethylene concentration in the mixture is only about 30 wt %.
Because orthochlorotoluene is a very good solvent, mixtures of
perchloroethylene with orthochlorotoluene and monochlorotoluene have good
solvency properties that are comparable to the solvency properties of
1,1,1-trichloroethane. In addition, the mixture of perchloroethylene and
monochlorotoluene is of low toxicity and is not known, at the present
time, to be carcinogenic, and neither perchloroethylene nor
monochlorotoluene has been identified as a compound that destroys ozone.
I have further discovered that mixtures of perchloroethylene and
monochlorotoluene display another unusual and unexpected property in that
the mixtures freeze at a significantly lower temperature than does either
perchloroethylene or monochlorotoluene. While mixtures of various organic
solvents sometimes freeze at a lower temperature than either solvent in
the mixture, the depression in the freezing point of mixtures of
perchloroethylene with monochlorotoluene is significantly lower than the
depression in the freezing point of mixtures of some similar organic
solvents.
DESCRIPTION OF THE INVENTION
The accompanying drawing is a graph comparing the flammability of mixtures
of perchloroethylene with various other solvents at different temperatures
and in different proportions. The drawing is further explained in Example
1.
The compositions of this invention can be formed by mixing about 25 to
about 85 wt % perchloroethylene with about 15 to about 75 wt %
monochlorotoluene. If the composition contains less than about 25 wt %
perchloroethylene, it will have a flash point below its boiling point and
will be combustible, and if more than about 85 wt % of the composition is
perchloroethylene, it will not be as good a solvent. The preferred range,
for the best properties, is about 30 to about 75 wt % perchloroethylene
and about 25 to about 70 wt % monochlorotoluene. If the composition is to
be used in a closed container or the perchloroethylene that evaporates
from the composition is captured and returned to the composition, the
composition preferably is about 30 to about 40 wt % perchloroethylene and
about 60 to about 70 wt % monochlorotoluene, in order to maximize its
solvency properties while retaining its non-flammability. However, if the
perchloroethylene is permitted to evaporate from the composition and is
not returned to it, the composition is preferably about 70 to about 85 wt
% perchloroethylene and about 15 to about 30 wt % monochlorotoluene so
that sufficient perchloroethylene is always present in the evaporating
composition to prevent it from igniting below its boiling point.
Perchloroethylene, Cl.sub.2 C.dbd.CCl.sub.2, is also known as
tetrachloroethene. Monochlorotoluene has the formula
##STR1##
While the chlorine group may be in either the ortho, meta, or para
positions, or mixtures of these positions, it is preferable to use
orthochlorotoluene (o-chlorotoluene), parachlorotoluene (p-chlorotoluene),
or mixtures thereof as those solvents are currently being manufactured in
large amounts. For example, a 50/50 wt % mixture of ortho and para
chlorotoluene is sold by Occidental Chemical Corporation under the trade
designation "AG 125" and a mixture of 97 to 9 wt % o-chlorotoluene and 1
to 3 wt % p-chlorotoluene is sold by Occidental Chemical Corporation under
the trademark "Halso 99."
In order to alter the properties of the mixture, it may be desirable to add
other components to it. For example, the
perchloroethylene-monochlorotoluene mixture can be mixed with about 1 to
about 50 wt % (based on the weight of the
perchloroethylene-monochlorotoluene mixture) of methylene chloride or
trichloroethylene. The presence of methylene chloride is useful in
increasing the evaporation rate of the mixture for applications such as
adhesives. The presence of trichloroethylene increases the solvency of the
composition and enables it to dissolve additional organic compounds or a
higher percentage of an organic compound.
The following examples further illustrate this invention.
EXAMPLE 1
Perchloroethylene was mixed with various other solvents and the mixtures
were tested for flash point using ASTM test D-5687, known as the Tag
Closed Tester. The results of these tests are shown on the accompanying
drawing. The ordinate gives the temperature of the mixture when it flashed
and the abscissa gives the volume% of perchloroethylene in the mixture.
Curve A is a mixture with Halso 99 monochlorotoluene, curve B is a mixture
with a high-boiling (360.degree. C.) hydrocarbon blend sold by Shell Oil
Company as "Shell 360," curve C is a mixture with a petroleum distillate
(ASTM D-484-52) known as "Stoddard Solvent," and curve D is "VM & P
Naphthas", (varnish makers and painters), a partly refined or unrefined
petroleum product. Curve E is the approximate boiling point of the
mixtures. The drawing shows that only mixtures of perchloroethylene and
monochlorotoluene had a flash point above the boiling point, which means
that that mixture did not have a flash point. The drawing also shows that
only about 22.4 to about 26.6 volume % (about 30 to about 35 wt %) of
perchloroethylene was required in the mixture with monochlorotoluene to
produce a mixture that did not have a flash point. Similar results were
obtained using ASTM test D92-85, known as the Cleveland Open Cup test.
EXAMPLE 2
The freezing points of perchloroethylene, Halso 99 monochlorotoluene, and
mixtures thereof are given in the following table:
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Composition (wt %) Freezing Point
Perchloroethylene
Halso 99 Halso 125 (.degree.C.)
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100 0 0 -22
0 100 0 -40
35 0 65 -32 to -57
35 65 0 -59 to -62
0 0 100 -24.5
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The table shows that the freezing point of the mixture was depressed by an
unusually large amount.
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