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Description  |
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The invention relates to azeotropic and pseudoazeotropic compositions
comprising a fluoro ether and to the uses of these compositions,
especially as a solvent, as a swelling agent or as a refrigerant fluid.
Fully halogenated chlorofluoro solvents (CFCs) such as
1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) are widely employed in
industry for degreasing and cleaning various surfaces, especially in the
case of delicate and complicated components and those difficult to clean.
The solvents can be used in various ways, in most cases involving at least
one stage in vapour phase.
CFC-113 is often employed for cleaning printed circuit boards and for
cleaning or degreasing precision components, especially in optics,
mechanics or electronics. CFC-113 is employed either pure or mixed with
other compounds, especially alkanes, alcohols or esters which increase the
solvent power of the product. The use of mixtures of azeotropic type is
then advantageous, since the composition of the bath does not vary with
time or during the various stages of the cleaning process.
Various compositions based on CFC-113 are also traditionally employed as a
drying agent, in order to remove the water adsorbed at the surface of
delicate components.
In processes for the preparation of cellular polymeric materials, such as
polyurethane foams, trichlorofluoromethane (CFC-11),
dichlorodifluoromethane (CFC-12) and, to a lesser extent,
chlorodifluoromethane (HCFC-22), trichlorotrifluoroethane (CFC-113) and
dichlorotetrafluoroethane (CFC-114) have for a long time been employed as
a blowing agent. Because of its very low thermal conductivity, CFC-11
makes it possible to obtain rigid polyurethane foams which are
particularly insulating and which are extensively employed as thermal
insulators, especially in the fields of construction, refrigeration and
transport. The use of chlorofluoroalkanes as a swelling agent in the
processes for the preparation of these cellular materials is well known.
CFC-11 and other fully halogenated chlorofluoroalkanes are also
traditionally employed as refrigerant fluids in some refrigeration
compressors.
However, fully halogenated chlorofluoroalkanes (CFCs) which are
conventionally employed as cleaning agents, as swelling agents or as
refrigerants are today suspected of causing environmental problems
associated with the destruction of the stratospheric ozone layer. The
effect which a product can have on the ozone layer has been quantified,
starting with complex mathematical models, as its ozone destruction
potential (ODP) and is expressed in relation to the ODP of CFC-11. A
worldwide agreement, "The Montreal Protocol", signed in September, 1987,
called for a reduction in the usage and production of CFCs with, in the
long term, a ban on their use. Consequently, there is at present an urgent
need to find new cleaning agents, new blowing agents and new refrigerants
which have little or no effect on the ozone layer.
To this end, a number of azeotropic compositions based on some
chlorofluorocarbons which are not fully halogenated, known by the generic
term of hydrochlorofluorocarbons (HCFCs) or hydrofluoroalkanes (HFAs),
such as 1,1-dichloro-1-fluoroethane (HCFC-141b) or
2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) mixed with each other or
especially with methanol or ethanol, have been proposed (EP-A-325,265,
EP-A-389,133, EP-A-392,668, W089/10,984, W089/12,118). The ODP of
HCFC-141b is equal to approximately 0.1 and that of HCFC-123 is of the
order of 0.02. Thus, these products already represent a very considerable
step forward in relation to traditional CFCs. Patent Application
EP-A-416,777 describes a process for the preparation of polymer foams with
a fluoro ether as blowing agent. This application does not, however,
disclose any azeotropic compositions.
One of the objectives of the present invention is to provide new azeotropic
or pseudoazeotropic compositions exhibiting a very low ODP and capable of
being employed especially as a cleaning agent, a blowing agent for
cellular polymeric materials or else as a refrigerant fluid, replacing
fully halogenated chlorofluoroalkanes suspected of attacking the
stratospheric ozone layer.
The present invention relates to azeotropic or pseudoazeotropic
compositions comprising difluoromethoxy-2,2,2-trifluoroethane and at least
one compound chosen from 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) and
1,1-dichloro-1-fluoroethane(HCFC-141b).
Difluoromethoxy-2,2,2-trifluoroethane appears particularly advantageous in
respect of its impact on the environment, since it exhibits a zero ODP
because of the absence of chlorine in its molecular structure. The
presence of difluoromethoxy-2,2,2-trifluoroethane in the compositions
according to the invention therefore makes it possible to reduce their ODP
accordingly.
An azeotropic or pseudoazeotropic composition is intended to mean any
mixture of two or more substances of a virtually constant boiling point,
which behaves like a pure substance, that is to say in which the
composition of the vapour produced by evaporation or by distillation is
substantially identical to the composition of the liquid mixture. In
practice these azeotropes or pseudoazeotropes with a virtually constant
boiling point, either or minimum or maximum, cannot therefore be separated
by simple distillation or by preferential evaporation.
The thermodynamic state of a fluid is fundamentally defined by four
interdependant variables: the pressure (P), the temperature (T), the
composition of the liquid phase (X) and the composition of the gaseous
phase (Y). An azeotrope or a pseudoazeotrope is a particular system
containing 2 or more components, in the case of which, at a given
temperature and at a given pressure, X is substantially equal to Y. The
compositions according to the invention are characterised by their
composition observed at atmospheric pressure. It goes without saying that
this does not limit the compositions according to the invention to these
particular compositions; all compositions comprising
difluoromethoxy-2,2,2-trifluoroethane and at least one compound chosen
from 2,2-dichloro-1,1,1-trifluoroethane and 1,1-dichloro-1-fluoroethane
exhibiting an azeotropic or pseudoazeotropic character as defined above
are covered by the invention, whatever the pressure at which these
compositions are used. It is, in fact, well known for the composition and
the boiling point of an azeotrope containing 2 or more constituents to
vary as a function of the chosen pressure conditions.
It has been found that liquid mixtures of
difluoromethoxy-2,2,2-trifluoroethane and of HCFC-123 and liquid mixtures
of difluoromethoxy-2,2,2-trifluoroethane and of HCFC-141b produce, by
evaporation, a vapour whose composition is substantially identical with
that of the liquid mixture. Consequently, the evaporation of these
mixtures, be it natural or forced by boiling or by pressure release, does
not produce any significant separation of the compositions into their
components. Furthermore, it has been observed that these mixtures boil at
a temperature which is lower than the boiling points of their components.
Mixtures of difluoromethoxy-2,2,2-trifluoroethane (boiling point at
atmospheric pressure of approximately 29.8.degree. C.) and of
2,2-dichloro-1,1,1-trifluoroethane (boiling point at atmospheric pressure
of approximately 27.8.degree. C.) boil at atmospheric pressure at a
temperature of approximately 27.0.degree..+-.1.degree. C. Mixtures of
difluoromethoxy-2,2,2-trifluoroethane and of 1,1-dichloro-1-fluoroethane
(boiling point at atmospheric pressure of approximately 31.7.degree. C.)
boil at atmospheric pressure at a temperature of approximately
28.5.degree..+-.1.degree. C.
The binary mixtures consisting of approximately 5 to 95% by weight of
difluoromethoxy-2,2,2-trifluoroethane and of approximately 95 to 5% by
weight of 2,2-dichloro-1,1,1-trifluoroethane form azeotropes or
pseudoazeotropes according to the invention. The azeotropes or
pseudoazeotropes formed by the binary mixtures consisting of approximately
20 to 80% by weight of difluoromethoxy-2,2,2-trifluoroethane and of
approximately 80 to 20% by weight of 2,2-dichloro-1,1,1-trifluoroethane
are preferred. The azeotropes or pseudoazeotropes formed by binary
mixtures consisting of approximately 30 to 65% by weight of
difluoromethoxy-2,2,2-trifluoroethane and of approximately 70 to 35% by
weight of 2,2-dichloro-1,1,1-trifluoroethane are particularly preferred.
At atmospheric pressure the binary composition consisting of approximately
45% by weight of difluoromethoxy-2,2,2-trifluoroethane and of
approximately 55% by weight of 2,2-dichloro-1,1,1-trifluoroethane forms a
true azeotrope whose boiling point is approximately 26.0.degree. C. This
composition is very particularly preferred.
Binary mixtures consisting of approximately 5 to 95% by weight of
difluoromethoxy-2,2,2-trifluoroethane and approximately 95 to 5% by weight
of 1,1-dichloro-1-fluoroethane form azeotropes or pseudoazeotropes
according to the invention. The azeotropes or pseudoazeotropes formed by
the binary mixtures consisting of approximately 30 to 85% by weight of
difluoromethoxy-2,2,2-trifluoroethane and approximately 70 to 15% by
weight of 1,1-dichloro-1-fluoroethane are preferred. Azeotropes or
pseudoazeotropes formed by binary mixtures consisting of approximately 45
to 75% by weight of difluoromethoxy-2,2,2-trifluoroethane and
approximately 55 to 25% by weight of 1,1-dichloro-1-fluoroethane are
particularly preferred. At atmospheric pressure the binary composition
consisting of approximately 61% by weight of
difluoromethoxy-2,2,2-trifluoroethane and approximately 39% by weight of
1,1-dichloro-1-fluoroethane forms a true azeotrope whose boiling point is
approximately 27.5.degree. C. This composition is very particularly
preferred.
Small quantities of other additives may also be added to the compositions
according to the invention. Thus, the latter may have added to them
stabilisers, surface-active agents or any other additives which make it
possible to improve their performance in use. The possible other additives
are added in a proportion of approximately 0.001 to 5% by weight of the
azeotropic or pseudoazeotropic mixture.
The invention also relates to the use of the azeotropic or pseudoazeotropic
compositions according to the invention, comprising
difluoromethoxy-2,2,2-trifluoroethane and at least the compound chosen
from 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) and
1,1-dichloro-1-fluoroethane (HCFC-141b) as cleaning agent, in particular
as solvent, as degreasing agent, as defluxing agent or as drying agent.
The invention also relates to the use of the azeotropic or
pseudoazeotropic compositions according to the invention as a blowing
agent for the preparation of cellular polymeric materials, as a
refrigerant fluid or as a propellent gas for packaging under pressure.
As a result of their azeotropic or pseudoazeotropic nature, the
compositions according to the invention can be used in any application
without any separation of these compositions into their constituents
taking place by evaporation or by distillation. The azeotropic character
of these compositions is particularly advantageous when they are employed
in cleaning processes using a solvent. These compositions exhibit very
good compatibility with the various types of surfaces to be treated, be
they made of metal, plastic or glass.
The compositions according to the invention are suitable for any cold
cleaning operation or for cleaning surfaces with vapour.
The compositions according to the invention also appear particularly
effective in processes for cleaning printed circuit boards, which
processes are intended to remove from the surface of these boards the
pickling flux employed in the stage of soldering of electronic components
and its residues. Traditional brazing fluxes consist of rosin, employed by
itself or with certain activators. The fluxes and their residues are
removed from the surface of the printed circuit board in a particularly
effective and selective manner with the compositions according to the
invention, even when these fluxes are highly activated. The azeotropic or
pseudoazeotropic compositions according to the invention have, in fact, a
high solvent power for flux and its residues without, however, damaging
the material forming the board substrate or the electronic components
arranged thereon. In addition, the compositions according to the invention
offer certain characteristics, especially of viscosity and surface
tension, which are particularly well suited to this application.
The compositions according to the invention can also be employed in any
other process as a replacement for compositions based on CFC-113. They are
particularly well suited as a drying agent, that is to say for removing
the water adsorbed at the surface of solid objects which require a
particularly clean surface, such as printed circuits, silicon wafers,
optical glasses, clock components and any other precision components.
The compositions according to the invention can also be employed as a
blowing agent in any process for the preparation of a cellular polymeric
material by polymerisation, polycondensation or polyaddition of the
reactants in the presence of a blowing agent or by blowing a
prepolymerised thermoplastic material with the aid of a blowing agent. It
has been found that the compositions according to the invention are
excellent blowing agents for the production of cellular polymeric
materials, in particular for those based on polyurethane. The quantity of
foams produced when employing these blowing agents is substantially
identical to that of the products obtained conventionally, for example
with the aid of CFC-11. The compositions according to the invention are
particularly well suited for the production of flexible, semi-rigid or
rigid foams based on polyisocyanates, such as polyurethane foams and
polyisocyanurate foams. They can also be employed for the preparation of
other cellular polymeric materials based, for example, on polyolefins,
polyvinyl chloride, polystyrene or phenolic resins. Various well-known
application techniques allowing these cellular materials to be
manufactured are described, for example, in the "Encyclopedia of Polymer
Science and Engineering", Vol. 3, 1985, pages 1 to 60.
As a result of their azeotropic or pseudoazeotropic nature, the
compositions according to the invention can also be employed as
refrigerant fluids in some refrigeration compressors, such as the
centrifugal "chillers".
The examples below, which do not imply any limitation, illustrate the
invention in a more detailed manner.
EXAMPLE 1
A glass distillation apparatus consisting of a boiler flask supporting a
reflux condenser was employed to demonstrate the existence of azeotropic
or pseudoazeotropic compositions between
difluoromethoxy-2,2,2-trifluoroethane and 1,1-dichloro-1-fluoroethane. The
temperature of the liquid is measured with the aid of a thermometer
immersed in the flask.
25 ml of pure difluoromethoxy-2,2,2-trifluoroethane are heated to boiling
at atmospheric pressure and small quantities of
1,1-dichloro-1-fluoroethane are then gradually introduced into the flask
with a graduated syringe via a side tube fitted with a septum.
The determination of the azeotropic composition is performed by recording
the change in the boiling temperature of the mixture as a function of its
composition. The composition in the case of which a minimum or maximum
boiling point is observed is the azeotropic composition at atmospheric
pressure.
The influence of atmospheric pressure on the boiling temperature of the
mixtures is corrected with the aid of the following formula:
tc=tr+0.00012 (760-P) (273+tr)
with
tr, the recorded temperature in .degree.C.
tc, the corrected temperature in .degree.C.
P, the atmospheric pressure at the time of measurement, in mm Hg.
The corrected boiling temperatures obtained for various compositions of
difluoromethoxy-2,2,2-trifluoroethane and of 1,1-dichloro-1-fluoroethane
are collated in Table I.
The best estimate of the composition in the case of which the boiling point
is lowest is approximately 61% by weight of
difluoromethoxy-2,2,2-trifluoroethane. The boiling point is 27.7.degree.
C..+-.0.2.degree. C. in the case of compositions containing approximately
43 to 80% by weight of difluoromethoxy-2,2,2-trifluoroethane.
TABLE I
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Weight fraction of Boiling
CF.sub.3 --CH.sub.2 --O--CHF.sub.2 in
temperature
the mixture (.degree.C.)
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100 29.8
98.21 29.6
94.80 29.2
90.12 28.9
84.55 28.2
79.63 27.9
75.25 27.8
71.35 27.5
67.79 27.6
63.11 27.6
59.02 27.5
55.43 27.5
51.28 27.5
47.70 27.6
44.41 27.7
42.88 27.9
40.07 28.1
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EXAMPLE 2
This example illustrates the azeotrope based on
difluoromethoxy-2,2,2-trifluoroethane and
2,2-dichloro-1,1,1-trifluoroethane, demonstrated with the aid of the
procedure described in Example 1, but this time progressively adding small
quantities of difluoromethoxy-2,2,2-trifluoroethane to 40 ml of
2,2-dichloro-1,1,1-trifluoroethane. The corrected boiling points for
various compositions by weight of difluoromethoxy-2,2,2-trifluoroethane
and of2,2-dichloro-1,1,1-trifluoroethane are collated in Table II.
The best estimate of the composition in the case of which the boiling point
is lowest is approximately 45% by weight of
difluoromethoxy-2,2,2-trifluoroethane. The boiling point is 26.2.degree.
C..+-.0.2.degree. C. for compositions containing approximately 25 to 65%
by weight of difluoromethoxy-2,2,2-trifluoroethane.
TABLE II
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Weight fraction of Boiling
CF.sub.3 --CH.sub.2 --O--CHF.sub.2 in
temperature
the mixture (.degree.C.)
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0 27.8
4.51 27.4
8.64 27.3
12.42 27.2
15.91 27.0
17.55 26.8
19.12 26.6
22.10 26.6
23.51 26.5
24.87 26.4
26.17 26.3
29.85 26.2
32.35 26.2
34.68 26.2
36.86 26.1
38.06 26.0
39.22 26.1
41.40 26.1
44.38 26.0
48.36 26.1
50.33 26.2
55.43 26.2
58.21 26.3
62.13 26.4
64.16 26.4
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EXAMPLES 3 TO 8
Various rigid polyurethane foams were prepared with various blowing agents,
starting with the same single formulation containing a polymeric
diphenylmethane isocyanate (MDI) and a mixture of an animated
sucrose-based polyol, of a brominated polyol polyether IXOL B 251 and of a
hydroxylated crosslinking agent. The diphenylmethane diisocyanate and the
polyols are introduced in ratios such that the value 110 is reached. The
formulation additionally contains a small quantity of silicone surfactant,
of phosphorus-containing flame-retardant additive and of amine catalyst.
The blowing agents employed are the following: Example 1: 40% by weight of
difluoromethoxy-2,2,2-trifluoroethane 60% by weight of
1,1-dichloro-1-fluoroethane Example 2: 40% by weight of
difluoromethoxy-2,2,2-trifluoroethane 60% by weight of
2,2-dichloro-1,1,1-trifluoroethane Example 3C: 100% by weight of
1,1-dichloro-1-fluoroethane (HCFC-141b) Example 4C: 100% by weight of
2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) Example 5C: 100% by weight
of trichlorofluoro-methane (CFC-11)
The foams are prepared by thorough mixing of all the ingredients for 15
seconds by means of a multiblade-type stirrer rotating at a speed of 1600
revolutions per minute, followed by pouring the mixture into a closed
20.times.20.times.10 cm mould.
The formulations used and the properties of the various foams obtained are
collated in Table III.
TABLE III
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EXAMPLE No.
1 2 3(C) 4(C)
5(C)
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FORMULATION (parts by weight)
MDI, value 110
Polyols 90 90 90 90 90
Crosslinking agent
7 7 7 7 7
Flame-retardant agent
5 5 5 5 5
Silicone surfactant
1 1 1 1 1
Water 1.15
1.15
1.15 1.15
1.15
Amine catalyst 1.4 1.4 1.4 1.4 1.4
CF.sub.3 --CH.sub.2 --O--CHF.sub.2
14 15.6
-- -- --
CFCl.sub.2 --CH.sub.3 (HCFC-141b)
21 -- 32 -- --
CF.sub.3 --CHCl.sub.2 (HCFC-123)
-- 23.4
-- 38 --
CFCl.sub.3 (CFC-11)
-- -- -- -- 36
FOAM CHARACTERISTICS
Density, kg/m.sup.3
raw, in closed mould
40.7
40.4
41 40.6
40
net, in closed mould
33.6
33.5
33.7 33.6
33.4
Thermal conductivity
after 1 day, W/m K
0.021
0.021
0.020
0.020
0.019
after 2 weeks, W/m K
0.022
0.023
0.023
0.022
0.021
Cell structure fine
fine
fine fine
fine
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