Note: Descriptions are shown in the official language in which they were submitted.
CA 02309694 2000-OS-10
WO 99lZ6907 PCT/GB98/03408
Preparation of Fluorine-containing Organic Compounds
The present invention relates to a process for the preparation of
fluorine-containing organic compounds by reacting a haloalkene with hydrogen
fluoride,
particularly to a process for the preparation of hydrofluorocarbons from
fluoroalkenes,
more particularly to a process for the preparation of 1,1,1,2,3,3,3-
heptafluoropropane
from hexafluoropropene, azeotropes or azeotrope-like mixtures of a
hydrofluorocarbonlhydrogen fluoride, particularly azeotropes or azeotrope-like
mixtures
of 1,1,1,2,3,3,3-heptafluoropropane/hydrogen fluoride and azeotropes or
azeotrope-like
mixtures of a haloalkene/hydrogen fluoride, particularly azeotropes or
azeotrope-like
mixtures of hexafluoropropene/hydrogen fluoride.
Hydrofluorocarbons are widely used as replacements for chIorofluorocarbon
compounds in a variety of applications. Such applications include use in
medical
applications, for example as an aerosol propellant, use as a fire suppressant,
use in
refrigeration applications and in other applications. 1,1,1,2,3,3,3-
heptafluoropropane,
which is known in the art as Hydrofluorocarbon 227ea and will hereinafter be
referred to
as "HFC 227ea" for convenience, has zero ozone depletion potential and is
particularly
beneficial in medical applications in the light of its combination of
properties including
low toxicity, non-flammability, solvent properties and boiling point.
It is known to produce hydrofluorocarbons by the hydrofluorination of a
fluoroalkene to the corresponding hydrofluoroalkane, optionally in the
presence of a
catalyst, in the liquid phase or vapour phase. Hydrogen fluoride is known for
use as a
hydrofluorination agent in such hydrofluorination processes.
A variety of materials may be employed as catalysts in such hydrofluorination
processes.
For example, in the vapour phase reaction of fluoroalkenes with hydrogen
fluoride for the preparation of hydrofluorocarbons, eg HFC 227ea from
hexafluoropropene, DE 2712732 and GB 902590 disclose the use of a chromium
oxyfluoride catalyst and an activated carbon catalyst respectively.
For example, in the liquid phase reaction of fluoroalkenes with hydrogen
fluoride
for the preparation of hydrofluorocarbons, eg HFC 227ea from
hexafluoropropene, WO
CA 02309694 2000-OS-10
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97/11042 and WO 96/0243 disclose the use of catalysts comprising an organic
amine
complexed with hydrogen fluoride and certain antimony catalysts respectively.
The disclosures in the aforementioned patent specifications are incorporated
herein by way of reference.
A stoichiometric excess of hydrogen fluoride to fluoroalkene is normally
employed in the aforementioned processes and the degree of conversion of
fluoroalkene
to hydrofluorocarbon is dependent on inter alia the catalyst employed, if any,
and the
conditions in the reactor, etc.
The product from such reactions typically comprises the desired
fluorine-containing organic compound, organic by-products and hydrogen
fluoride. For
example, where the haloalkene is hexafluoropropene, which will hereinafter be
referred
to as "HFP" for convenience, the product stream leaving the reactor in which
HFP is
reacted with hydrogen fluoride typically contains HFC 227ea, HFP, hydrogen
fluoride
and azeotropes thereof.
It is normal practice to recover as much as possible of the hydrogen fluoride
from the product stream from such hydrofluorination reactions for re-use. This
may be
partially achieved by distillation. However, the presence in the product
stream of an
azeotrope or azeotrope-like mixture of HFC 227ea/hydrogen fluoride and an
azeotrope
or azeotrope-like mixture of HFP/hydrogen fluoride limits the extent to which
hydrogen
fluoride can be separated from the fluoro-organic compounds by simple
distillation.
It is known that the stream comprising the hydrofluorocarbon/hydrogen fluoride
azeotrope, eg HFC 227ea/hydrogen fluoride azeotrope, and the
haloalkene/hydrogen
fluoride azeotrope, eg HFP/hydrogen fluoride azeotrope, after recovery of a
portion of
the hydrogen fluoride by distillation, can be water-washed to allow recovery
of both a
mixture of organic compounds essentially free of hydrogen fluoride and aqueous
hydrogen fluoride. However, such a treatment is wasteful of hydrogen fluoride
since it is
normal practice for aqueous hydrogen fluoride generated in this way to be
neutralised
with caustic solution and/or lime and ultimately disposed of.
Alternatively, the product stream from the reaction of a haloalkene with
hydrogen fluoride, after recovery of a portion of the hydrogen fluoride by
distillation,
may be treated with a solution of alkali metal dissolved in anhydrous hydrogen
fluoride
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wo 99n69o~ Pcncs98io3ao~
as described in our patent specification WO 97/I3I79. However, although such a
process recovers hydrogen fluoride for re-use within the process, it has the
disadvantage
of requiring additional equipment.
Furthermore, it is known that in the preparation of fluorine-containing
organic
compounds by the reaction of a haloalkene with hydrogen fluoride the
haloalkene/hydrogen fluoride azeotrope can be separated from the fluorine-
containing
compound/hydrogen fluoride azeotrope by fractional distillation and hydrogen
fluoride
can be removed from the fluorine-containing organic compound/hydrogen fluoride
azeotrope by treatment with water. However, treatment of the fluorine-
containing
organic compound/hydrogen fluoride azeotrope with water to remove hydrogen
fluoride
therefrom involves the use of expensive equipment and is wasteful of hydrogen
fluoride.
It will be appreciated that whereas aqueous~scrubbing is an effective way of
removing hydrogen fluoride from the organic compounds) after reacting hydrogen
fluoride with a haloalkene aqueous scrubbing tends to be expensive in terms of
hydrogen
fluoride loss from the process. Preferably as much as possible, more
preferably
essentially all, of the hydrogen fluoride is separated from the product stream
before
aqueous scrubbing and particularly more preferably aqueous scrubbing is
avoided.
Where in the preparation of a fluorine-containing organic compound by the
reaction of a haloalkene with hydrogen fluoride the haloalkene/hydrogen
fluoride
azeotrope is more volatile, ie has a lower boiling point, than the fluorine-
containing
organic compound/hydrogen fluoride azeotrope produced in the reaction we have
now
found that by (a) charging the reaction product to a distillation column, (b)
introducing
the haloalkene into the distillation column and (c) distilling the resulting
mixture both
the fluorine-containing organic compound substantially free of hydrogen
fluoride and
the haloalkene/hydrogen fluoride azeotrope can be separated.
The separated haloalkene/hydrogen fluoride azeotrope can be recycled to the
reaction vessel, can be used in another reaction or preferably at least a
portion thereof is
separated into a haloalkene-rich liquid phase and a hydrogen fluoride-rich
liquid phase
as is hereinafter more fully described.
According to the first aspect of the present invention there is provided a
process
for the preparation of a fluorine-containing organic compound by reacting a
haloalkene
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with hydrogen fluoride wherein both the fluorine-containing organic compound
and the
haloalkene separately form azeotropes with hydrogen .fluoride and wherein the
haloalkene/hydrogen fluoride azeotrope is more volatile than the fluorine-
containing
organic compound/hydrogen fluoride azeotrope characterised by the Steps of
A. charging the haloalkene and the mixture comprising the
fluorine-containing organic compound/hydrogen fluoride azeotrope, or
azeotrope-like mixture, and optionally the haloalkene/hydrogen fluoride
azeotrope, or azeotrope-like mixture, and/or hydrogen fluoride arising from
the
reaction of the haloalkene with hydrogen fluoride to a distillation column
B. recovering the haloalkene/hydrogen fluoride azeotrope, or azeotrope-like
mixture, and the fluorine-containing organic compound from the distillation
column separately; and
C. optionally separating at least a portion of the haloalkene/hydrogen
fluoride azeotrope, or azeotrope-like mixture, recovered from Step B into a
haloalkene-rich liquid phase and a hydrogen fluoride-rich liquid phase.
The reaction of haloalkene with hydrogen fluoride mentioned in Step A of the
process according to the first aspect of the present invention may be carried
out in the
liquid phase or in the vapour phase, optionally in the presence of a suitable
catalyst.
Where Step C in the process according to the first aspect of the present
invention
is carried out separation is typically effected by allowing the haloalkene-
rich liquid
phase and the hydrogen fluoride-rich liquid phase to separate under gravity.
In a first embodiment of the process according to the first aspect of the
present
invention, the product of the reaction of the haloalkene with hydrogen
fluoride is
typically distilled to recover a portion of the hydrogen fluoride therefrom
before the
mixture comprising fluorine-containing organic compound/hydrogen fluoride
azeotrope
or azeotrope-like mixture thereof, haloalkene/hydrogen fluoride azeotrope or
azeotrope-like mixture thereof, and hydrogen fluoride is charged to the
distillation
column in Step A.
The portion of hydrogen fluoride recovered by distillation prior to Step A,
where
it is recovered, may be recycled to the reactor vessel.
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In a second embodiment of the process according to the first aspect of the
present
invention, the product of the reaction of the haloalkene with hydrogen
fluoride is
charged directly to the distillation column in Step A.
Any hydrogen fluoride which is present in excess of that required to form
azeotropes in the fluorine-containing organic compound recovered from Step B
may be
recovered, for example by distillation.
The haloalkene/hydrogen fluoride azeotrope, or azeatrope-like mixture thereof,
recovered from Step B may be fed directly to the reactor in which the
fluorine-containing organic compound is produced or to an appropriate process
streams)
thereto containing the haloalkene, for example a stream containing the mixture
of the
haloalkene and hydrogen fluoride.
Likewise, where Step C is carried out, the hydrogen fluoride-rich phase and/or
the haloalkene-rich phase recovered therefrom, may be fed directly to the
reactor in
which the fluorine-containing organic compound is produced or to an
appropriate
process streams) thereto containing the haloalkene, for example a stream
containing the
mixture of the haloalkene and hydrogen fluoride.
According to the second aspect of the present invention there is provided a
process for the preparation of a fluorine-containing organic compound by
reacting a
haloalkene with hydrogen fluoride wherein both the fluorine-containing organic
compound and the haloalkene separately form azeotropes with hydrogen fluoride
and
wherein the haloalkene/hydrogen fluoride azeotrope is more volatile than the
fluorine-containing organic compound/hydrogen fluoride azeotrope which process
comprises the steps of
A. charging a mixture comprising a haloalkene and hydrogen fluoride to a
reactor; and
B. optionally recovering at least a portion of hydrogen fluoride from the
reaction products from Step A by distillation
characterised by the further Steps of
C. charging the haloalkene and the mixture comprising the
fluorine-containing organic compound/hydrogen fluoride azeotrope, or
azeotrope-like mixture thereof, the haloalkene/hydrogen fluoride azeotrope, or
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azeotrope-like mixture thereof , and HF from the reactor in Step A or, where
Step
B is carried out, the haloalkene and the mixture comprising the
fluorine-containing organic compound/hydrogen fluoride azeotrope, or
azeotrope-like mixture thereof, and the haloalkene/hydrogen fluoride
azeotrope,
or azeotrope-like mixture thereof, from Step B to a distillation column;
D. recovering a haloalkene/hydrogen fluoride azeotrope, or azeotrope-like
mixture thereof, from the distillation column in Step C;
E. recovering the fluorine-containing organic compound substantially free
from hydrogen fluoride from the distillation column in Step C; and
F. optionally separating at least a portion of the haloalkene/hydrogen
fluoride azeotrope, or azeotrope-like mixture thereof, recovered in Step D
into a
haloalkene-rich phase and a hydrogen fluoride-rich phase.
In the process according to the second aspect of the present invention, where
Step F is carried out: the hydrogen fluoride-rich liquid phase can be recycled
to a
1 S reaction vessel for the reaction of haloalkene with hydrogen fluoride or
to a feed Iine
thereto; and at least a portion of the haloalkene-rich liquid phase can be
recycled to Step
C.
In the process according to the second aspect of the present invention the
haloalkene/hydrogen fluoride azeotrope, or azeotrope-like mixture thereof,
recovered
from the distillation column in Step D or the portion thereof not subjected to
Step F,
where Step F is carried out, may be recycled to the reaction vessel for the
reaction of
haloalkene and hydrogen fluoride or to a feed-line thereto.
According to a further aspect of the present invention there is provided an
azeotrope, or azeotrope-like mixture, of HFC 227ea and hydrogen fluoride.
According to a yet further aspect of the present invention there is provided
an
azeotrope, or azeotrope-like mixture, of HFP and hydrogen fluoride.
Where HFC 227ea is prepared by reacting HFP with hydrogen fluoride in the
process according to the second aspect of the present invention and where Step
A is
carried out in the liquid phase in the presence of a catalyst, eg TaFs, NbFs
or SbFs, it is
suitably carned out at a temperature in the range 20 to 200°C,
preferably 40 to 120°C
and especially 50 to 100°C. Suitably the reaction in Step A is carried
out at
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superatmospheric pressure such that the reactants are in the liquid phase for
sufficient
time to react to produce HFC 227ea. Preferably the pressure is at least 5 bar
and more
preferably the pressure is 10 to 50 bar.
The residence time in the reactor in Step A in the process according to the
second
aspect of the present invention is sufficient to permit conversion of
haloalkene feedstock
into fluorine-containing organic compound. The required residence time will be
dependent on inter alia the degree of conversion required, the reactant ratio
and the
reaction conditions.
Haloalkene from Step F in the process according to the second aspect of the
present invention is preferably recycled to the reactor in which the fluorine-
containing
organic compound is produced.
Where a low conversion rate of haloalkene into the fluorine-containing organic
compound is desired it is preferable that the feedstocks be recycled to
increase the yield
of the fluorine-containing organic compound from the starting material.
However, we
do not exclude the possibility that recycling is employed where high single
pass
conversions are required.
In Step A of the process according to the second aspect of the present
invention
the molar ratio of hydrogen fluoride (HF) to haloalkene fed to the reactor is
suitably at
least 1:1 and preferably 1.2 to 10:1. If a lower conversion rate is required a
molar ratio
of HF to haloalkene of 0.1 up to 1: I may be employed.
In Step A of the process according to the second aspect of the present
invention
the molar ratio of haloalkene to the catalyst is suitably not more than 100:1
and is
preferably 1 to 50:1.
The levels of HF, haloalkene and catalyst in Step A of the process according
to
the second aspect of the present invention are suitably selected such that the
catalyst and
reactants remain dissolved in the liquid phase under the reaction conditions
employed.
The process according to the second aspect of the invention may be operated in
batch or continuous mode as desired. Semi-batch operation may also be employed
in
which one or more feedstocks are fed continuously to the process and one or
more other
feedstocks are fed to the process in batch-wise fashion.
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Alternatively, the process according to the second aspect of the present
invention
may be carried out in the vapour phase. Suitable conditions and catalysts for
use in
carrying out the process according to the second aspect of the present
invention in the
vapour phase are more fully described in DE 2712732 and GB 902590 mentioned
S hereinbefore.
In Step C of the process according to the second aspect of the present
invention
and in Step A of the process according to the first aspect of the present
invention the
haloalkene and the mixture comprising fluorine-containing organic
compound/hydrogen
fluoride azeotrope, or azeotrope-like mixture thereof, haloalkene/hydrogen
fluoride
azeotrope, or azeotrope-like mixture thereof, are preferably simultaneously
charged to
the distillation column, and more preferably the haloalkene is charged to the
distillation
column at a point thereon below the point at which the mixture is charged
thereto.
The process according to the first or second aspect of the present invention
is
applicable to mixtures of hydrogen fluoride with any haloalkene and any
1 S fluorine-containing organic compound provided that the relative volatility
of the
haloalkene/hydrogen fluoride azeotrope, or azeotrope-like mixture thereof, is
higher than
that of the fluorine-containing organic compound/hydrogen fluoride azeotrope,
or
azeotrope-like mixture thereof. Most hydrofluorocarbons,
hydrochlorofluorocarbons and
hydrofluoroethers form azeotropes or azeotrope-like mixtures, or azeotrope-
like
mixtures, with hydrogen fluoride and the treatment of such mixtures is a
preferred
embodiment of the invention, especially the treatment of mixtures wherein the
fluorine=containing organic compound is a hydrofluorocarbon, a
hydrochlorofluorocarbon, a chlorofluorocarbon or a hydrofluoroether.
As examples of classes of fluorine-containing organic compounds which may be
prepared by the process according to the first aspect of the present invention
may be
mentioned inter alia hydrofluorocarbons (HFCs), eg pentafluoroethane and
tetrafluoroethane, and hydrochloro-fluorocarbons (HCFCs), eg
1,1,1,2-tetrafluoro-2-chloroethane.
As examples of fluorine-containing organic compounds which may be prepared
by the process according to the first aspect of the present invention may be
mentioned
inter alia 1,1,1,2-tetrafluoroethane [HFC 134a], chloro-1,1,1-trifluoroethane
[HCFC
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133a], chlorotetrafluoroethane [HCFC 124/124a], pentafluoroethane [HFC I25],
1,1-difluoroethane [HFC 152aJ, 1,1,1-trifluoroethane [HFC 143a] and
1,1,1,3,3-pentafluoropropane [HFC 245fa].
Where the fluorine-containing organic compound prepared by the process
according to the first aspect of the present invention is a hydrofluorocarbon,
hydrochlorofluorocarbon or chlorofluorocarbon it will usually contain from 1
to 6
carbon atoms and preferably from 1 to 4 carbon atoms.
The present invention will be further illustrated by reference to the
accompanying drawings which illustrate, by way of example only, schematic
representations of plants for carrying out the process according to the
present invention
or temperature/composition plots for certain binary systems.
In the drawings:
Figures 1, 2, 3 and 4 are schematic representations of plants for carrying out
the process
according to the second aspect of the present invention in which Figure 1
illustrates the
use of Steps A, B, C, D and E, Figure 2 illustrates the use of Steps A, B, C,
D, E and F,
Figure 3 illustrates the use of Steps A, C, D and E and Figure 4 illustrates
the use of
Steps A, C, D, E and F;
Figure 5 is a schematic representations of a plant for carrying out the second
embodiment of the process according to the first aspect of the present
invention;
Figure 6 is a temperature/composition plot for the HFC 227ea/HF binary; and
Figure 7 is a temperature/composition plot for the HFP/I-~ binary.
Although the processes according to the first and second aspects of the
present
invention are applicable to any of the aforementioned organic compounds they
will be
described hereinafter by reference to the preparation of HFC 227ea.
In Figures 1 and 2, feed pipe (1) leads to a reactor (4), which optionally
contains
a fluorination catalyst. Product pipe (5) from the reactor (4) is in fluid-
flow
communication with a frst distillation column (6), which is for example a
single stage
flash vessel. Distillation column (6) is typically operated at a pressure of
12 bars wj~th a
bottoms temperature of 70°C and a tops temperature of around
50°C. Bottoms pipe (2)
from distillation column (6) is in fluid-flow communication with feed-pipe
(1). Tops line
(7) from distillation column (6) is in fluid-flow communication with a second
distillation
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column (8), which is for example a packed column. Distillation column (8) is
typically
operated at a pressure of around 12 bars with a tops temperature of
37°C and a bottoms
temperature of around 60°C. Distillation column (8) is provided with a
feed line (9)
below the point at which tops line (7) is attached to it, a bottoms pipe (10)
and a tops
pipe (3) which is in fluid-flow communication with feed-pipe (1).
In Figure 2, tops pipe (3) from distillation column (8) is provided with a
line (1 I)
which is in fluid flow communication with phase separator (12). Phase
separator (12) is
provided with a line (13) in fluid-flow communication with feed line (9) and a
line (14)
in fluid-flow communication with tops line (3).
In operation, the reactor (4) is charged through feed pipe (1) with a feed
stream
containing fresh hydrogen fluoride, recycled hydrogen fluoride (from bottoms
line (2)
and tops line (3)) and HFP/hydrogen fluoride azeotrope (from tops line (3}).
The
product from reactor (4) (HFC 227ea, hydrogen fluoride and optionally
unconverted
HFP) travels through product pipe (5) to the first distillation column (6). In
distillation
I S column (6), hydrogen fluoride, which is recycled via bottoms line (2) to
feed pipe (1), is
separated from the mixture of HFC 227ea, hydrogen fluoride and unconverted
HFP. The
mixture of HFC 227ea, residual hydrogen fluoride and HFP is fed via tops line
(7) from
the distillation column (6) to the second distillation column (8}. HFP is fed
via feed line
(9) to column (8). A stream comprising HFP and essentially all the hydrogen
fluoride
content of the stream entering distillation column (8) via line (7) is removed
from the
top of distillation column (8) via line (3) and the product stream HFC 227ea
is removed
from the bottom of column (8) via bottoms lead (10).
Preferably, as shown in Figure 2, a portion of the stream in pipe (3) is
diverted in
the liquid phase through pipe (11) to separator (12) in which a HFP-rich phase
is
separated from an hydrogen fluoride-rich phase. The HFP-rich liquid phase is
fed via
line (13) to feed line (9) to distillation column (8). The hydrogen fluoride-
rich liquid
phase from separator (12) is returned via line (14) to tops pipe (3) to feed
line (1).
In Figures 3 and 4, feed pipe (21) leads to a reactor (22), which optionally
contains a fluorination catalyst. Product pipe (23) from the reactor (22) is
in fluid-flow
communication with a distillation column (24), which is for example a packed
column.
Distillation column (24) is typically operated at a pressure of around 12 bars
with a tops
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WO 99/26907 PCT/GB98/03408
temperature of 37°C and a bottoms temperature of around 60°C.
Distillation column
(24) is provided with a bottoms pipe (25), a tops pipe (26), which is in fluid-
flow
communication with feed-pipe (21), and feed line (27) below the point at which
product
pipe (23) is attached to it.
In Figure 4, tops pipe (26) from distillation column (24) is provided with a
line
(28) which is in fluid flow communication with phase separator (29). Phase
separator
(29) is provided with both line (30) in fluid-flow communication with Line
(26) and line
(3I) in fluid-flow communication with feed line (27).
in operation, the reactor (22) is charged through feed pipe (21) with a feed
stream containing hydrogen fluoride (fresh and recycled through a hydrogen
fluoride-rich stream (from line (26)) and recycled HFP. The product from
separator (29)
(HFC 227ea, hydrogen fluoride and optionally unconverted HFP) travels through
product pipe (23) to distillation column '(24). HFP is fed via feed line (27)
to column
(24). A stream comprising HFP and essentially all the hydrogen fluoride
content of the
stream entering distillation column (24) via line (23) is removed from the top
of
distillation column (24) via line (26) and the product stream HFC 227ea is
removed
from the bottom of column (24) via bottoms lead (25).
Preferably, as shown in Figure 4, a portion of the stream in pipe (26) is
diverted
in the liquid phase through pipe (28) to separator (29) in which a HFP-rich
phase is
separated from a hydrogen fluoride-rich phase. The HFP-rich phase from column
(24) is
fed via line (31 ) to feed line (27) to disti Nation column (24). The hydrogen
fluoride-rich
phase from separator (29) is returned via lines (30) and (26) to feed line
(21).
In Figure 5, distillation column (32) is provided with feed line (31)
connected to
a reactor (not shown), feed line (33), bottom line (34) and top line (35). In
operation, a
mixture comprising HFC 227ea/HF azeotrope, or azeotrope-like mixture, HFP/HF
azeotrope, or azeotrope-like mixtur a and/or HF is fed via line (31 ) to
distillation column
(32 ) and a stream comprising HFP is fed via line (33) to distillation column
(32).
HFP/HF azeotrope, or azeotrope-like mixture, is removed from distillation
column (32)
via top line (35) and HFC 227ea substantially free from HF is removed from
distillation
column (32) via bottom line (34).
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The present invention is further illustrated by reference to the following
Example.
The Example reveals that both HFP and HFC 227ea form azeotropes with HF
and, at constant pressure the boiling point of the HFP/1~ azeotrope is lower
than the
boiling point of the HFC 227ea/HF azeotrope.
A temperature/composition plot for the HFC 227ea/F-1F binary is illustrated in
Figure 6 wherein the dashed line ---- represents the vapour phase composition
and the
solid line represents the liquid phase composition. From Figure 6 it can be
seen that at
174psi the HFC 227ea/HF azeotrope has a boiling point of 123°F and a
composition of
42mole% HF and 58mole% HFC 227ea.
A temperature/composition plot for the HFP/HF binary is illustrated in Figure
7
wherein the dashed line ---- represents the vapour phase composition and the
solid line
represents the liquid phase composition. From Figure 7 it can be seen that at
174psi the
HFP/HF azeotrope has a boiling point of 98°F and a composition of
38mole% HF and
62mole% HFP.
25
12
