Note: Descriptions are shown in the official language in which they were submitted.
CA 02373437 2001-11-16
WO 00/69797 PCT/GB00/01861
Production of 1,1,1,2;3,3,3-heptafluoropropane
The present invention relates to a process for the production of
1,1,1,2,3,3,3-heptafluoropropane from hexafluoropropene and to a process for
the
separation of mixtures comprising 1,1,1,2,3,3,3-heptafluoropropane and
hydrogen
fluoride.
Hydrofluorocarbons are widely used as replacements for chlorofluorocarbon
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 hexafluoropropene, hereinafter
referred to as "HFP" for convenience, with hydrogen fluoride for the
preparation of
HFC 227ea, 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 HFP with hydrogen fluoride for
the
preparation of HFC 227ea, WO 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 HFP is normally employed in
the aforementioned processes and the degree of conversion of HFP to HFC 227ea
is
dependent on inter alia the catalyst employed, if any, and the conditions in
the reactor in
which the conversion is earned out.
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The product stream leaving the reactor typically comprises HFC 227ea, HFP,
hydrogen fluoride and a ternary azeotrope 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 HFC 227ea/hydrogen fluoride
azeotrope and the 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 fluoroalkene 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
as described in our patent specification WO 97/13179. 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
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WO 00/69797 PCT/GB00/01861
essentially all, of the hydrogen fluoride is separated from the product stream
before
aqueous scrubbing and particularly more preferably aqueous scrubbing is
avoided.
In our pending International Patent Application GB 98/03408 we disclose that
where in the preparation of a fluorine-containing organic compound by the
reaction of a
haloalkene with hydrogen fluoride, for example the production of HFC 227ea
from HFP,
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 both the fluorine-containing organic compound substantially free
of
hydrogen fluoride and the haloalkene/hydrogen fluoride azeotrope can be
separated by
charging the reaction product and the haloalkene to a distillation column and
distilling
the resulting mixture.
We have now found surprisingly that in the preparation of HFC 227ea by the
reaction of HFP with hydrogen fluoride the reaction product phase-separates in
the
liquid phase to afford an organic-rich phase, which comprises HFC 227ea and
HFP, and
1 S a hydrogen fluoride-rich phase. The mole fraction of HF to 227ea in the
reaction product
may be from about 0.1 to 0.9.
Furthermore, we have found that addition of HFP to the reaction product in the
liquid phase enhances the aforementioned phase-separation.
According to the first aspect of the present invention there is provided a
process
for the production of HFC 227ea by the reaction of HFP with hydrogen fluoride
characterised by the Steps of
A. charging the reaction mixture from the reaction of HFP with hydrogen
fluoride
to a liquid-phase separator and allowing an organic phase and a hydrogen
fluoride-rich phase to separate under gravity ;
B. recycling the hydrogen fluoride-rich phase separated in Step A to the
reactor in
which the reaction is carried out:
C. charging the organic-rich phase separated in Step A to a distillation
column;
D. recovering the HFC 227ea and an HF-rich mixture separately. from the
distillation column in Step (C); and
E. recycling the HF-rich mixture recovered from Step D to the reactor.
Preferably the reaction mixture charged to the liquid-phase separator in Step
(A)
comprises an HFC 227ea/HF azeotrope, or azeotrope-like mixture, and optionally
an
HFP/I~ azeotrope, or azeotrope-like mixture.
23-05-2001 GB 000001861
CA 02373437 2001-11-16
The reaction mixture charged to the liquid-phase separator in Step A rnay be
the
mixture arising directly from the reactor in which HFP is reacted with
hydrogen fluoride
(direct mixture). It is often preferred, however, that the mixture charged to
the
liquid-phase separator is essentially an HFC 227ea/hydrogen fluoride
azeotrope, for
example obtained from distillation of the direct mixture.
It will be appreciated that the whereas the use of an HFC 227ea/HF azeotrope,
or
azeotrope-like mixture, in the process according to the present invention will
not
facilitate separation of the organic phase from the hydrogen fluoride-rich
phase such use
increases the amount of HFC 227ea to be removed per pass and, accordingly,
reduces
the amount of material to be recycled.
We have found surprisingly that addition of HFP facilitates separation of the
HFC 227ea/hydrogen fluoride azeotrope into its components. The HFP may be
introduced into the process according to the present invention at one or more
appropriate
points. For example, it may be charged to the reactor and/or to the liquid-
phase separator
in Step A and/or to the distillation column in Step C. Preferably the HFP is
added to the
liquid phase separator, either directly or mixed with the reaction mixture.
The reaction of HFP with hydrogen fluoride ~rrtl~~essssasseg.~e-tie-first
,SPr~r inm~nti~ i may be carried out in the liquid phase or in the vapour
phase.
To facilitate the separation in Step A of the process seee~g-~e.~s~-es~eet
of the present invention~Step A is preferably carried out at below ambient
temperature,
typically at below 30°C.
To facilitate the separation in Step A of the process aeeer~~iing-~e-i~a-
f~s~~.~
of the present inventions Step A is preferably carried out at supra-
atmospheric pressure,
typically 1-20 bars and preferably about 10 bars.
v v a a
i~entier~'~e product of the reaction of HFP with hydrogen fluoride 'r~~
distilled to
recover a portion of the hydrogen fluoride therefrom before the mixture
comprising HFC
227ea/hydrogen fluoride azeotrope or azeotrope-like mixture thereof,
HFP/hydrogen
fluoride azeotrope or azeotrope-like mixture thereof, and hydrogen fluoride is
charged to
the liquid phase separator in Step A.
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CA 02373437 2001-11-16
The portion of hydrogen fluoride recovered by distillation in a recovery step
prior to Step A, where such a recovery step is carried out, is preferably
recycled to the
reactor vessel.
..
~~the pro ~ct of the reaction of HFP with hydrogen fluorid ~~g d directly
to the liquid-phase separator in Step A.
Where HFC 227ea is prepared by reacting HFP with hydrogen fluoride in the
liquid phase in the
presence of a catalyst, eg TaFs, NbFs or SbFs, it is suitably carried 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 is carried out at 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.
residence time in the reactor i f
tl~r~ i~ sufficient to permit conversion of HFP feedstock into HFC
227e ~sThe r~~~ residence time will be de endent o int r
q p n a aha the degree of
conversion required, the reactant ratio and the reaction conditions.
Where a low conversion rate of HFP into HFC 227ea is desired it is preferable
that the feedstocks be recycled to increase the yield of HFC 227ea from the
starting
material. However, we do not exclude the possibility that recycling is
employed where
high single pass conversions are required.
I the molar ratio of hydrogen
fluoride (HF) to-HFP fed to the reactor is suitably at least 1:1 and
preferably between 1.2
and 10:1. It will be appreciated that where a molar ratio of HF to HFP of 0.1
up to 1:1 is
employed the conversion ratio and/or the yield will be lower.
'~e molar ratio of HFP to the
catalyst is suitably not more than 100:1 and is preferably between 1:1 and
50:1.
The levels of HF, HFP and catalyst in the process according to the present
invention are suitably selected such that the catalyst and reactants are at
least largely
dissolved in the liquid phase under the reaction conditions employed.
The process according to the present invention may be operated in batch or
continuous mode as desired. Semi-batch operation may also be employed in which
one
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AMENDED SHEET
23-05-2001 GB 000001861
CA 02373437 2001-11-16
or more feedstocks are fed continuously to the process and one or more other
feedstocks
are fed to the process in batch-wise fashion.
Alternative) ~ ~~ HF~~ ~F
y, e-px~c~ss-asser~~~;-te.t~e.pe~t~m may be carried out
in the vapour phase. Suitable conditions and catalysts for use in carrying out
the p~~
o~ H FQo..~.dl t1 F
accordmgtatbe_pteser~~ve~ie~t in the vapour phase are more fully described in
DE
2712732 and GB 902590 mentioned hereinbefore.
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.
In the drawings:
Figure 1 is a schematic representation of a plant wherein HFP is fed to the
liquid-phase
separator;
Figure 2 is a schematic representation of a plant wherein HFP is fed to the
reactor;
Figure 3 is a schematic representation of a plant wherein the product of the
reaction is
fed directly to the liquid-phase separator; and
Figure 4 is a ternary diagram illustrating HFC 227ea, HFP and HF separation.
In Figures 1 and 2, feed pipe (1) leads to a reactor (2), which optionally
contains
a fluorination catalyst. Product pipe (3) from the reactor (2) is in fluid-
flow
communication with a first distillation column (4), which is for example a
single stage
flash vessel. Distillation column (4) is typically operated at a pressure of
12 bars with a
bottoms temperature of 100°C and a tops temperature of around
SO°C. Bottoms pipe (5)
from distillation column (4) is in fluid-flow communication with feed-pipe
(1). Tops line
(6) from distillation column (4) is in fluid-flow communication with a liquid-
phase
separator (7). Tops line (8) from the liquid-phase separator {7) is in fluid-
flow
communication with feed-pipe (1). Bottoms line (9) from the liquid-phase
separator (7)
is in fluid-flow communication with a second distillation column (10), which
is for
example a packed column. Distillation column (10) is typically operated at a
pressure of
around 12 bars with a tops temperature of 37°C and a bottoms
temperature of around
GO°C. Distillation column (10) is provided with an exit pipe for
product (11 ) and a tops
pipe (12).
In Figure l, tops pipe (12) from distillation column (10) is in fluid flow
communication with tops line (6) which is provided with a feed-pipe (13).
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AMENDED SHEET
CA 02373437 2001-11-16
WO 00/69797 PCT/GB00/01861
In Figure 2, tops pipe (12) from distillation column (10) is in fluid flow
communication with feed-pipe (1) which is provided with feed-pipe (13).
In operation, in Figures l and 2, the reactor (2) is charged through feed pipe
(1)
with a feed stream containing fresh hydrogen fluoride and recycled hydrogen
fluoride
S (from lines (5) and (8) and, in Figure 2, line (12) ). The product from
reactor (2)
comprising HFC 227ea, hydrogen fluoride and unconverted HFP, often in the form
of a
ternary azeotrope, travels through product pipe (3) to the first distillation
column (4). In
distillation column (4), hydrogen fluoride, which is recycled via bottoms line
(5) 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 (6) from the distillation column (4) to the liquid-phase
separator (7).
The liquid-phase separator (7) is typically operated at 0-20°C to
afford better separation.
In Figure 1, HFP is fed via feed line (13) to liquid-phase separator (7). In
Figure 2, HFP
is fed via line (13) and feed-pipe (1) to reactor (2). In the liquid phase
separator (7), an
HF-rich phase separates from the organics-rich phase. The HF-rich phase is
returned via
tops-line (8) to feed-pipe ( 1 ) The organics-rich phase flows via bottoms
line (9) to
distillation column (10). A stream comprising HFP and essentially all the
hydrogen
fluoride content of the stream entering distillation column (10) via line (9)
is removed
from the top of distillation column (10) via line (12) and the product stream
HFC 227ea
is removed from the bottom of column (10) via exit pipe (11).
In Figure 3, feed pipe (1) leads to a reactor (2), which optionally contains a
fluorination catalyst. Line (14) from reactor (2) is provided with a feed line
(13) and is in
fluid-flow communication with a liquid-phase separator (7). Tops line (8) from
the
liquid-phase separator (7) is in fluid-flow communication with feed-pipe (1).
Bottoms
line (9) from the liquid-phase separator (7) is in fluid-flow communication
with a
distillation column (10), which is for example a packed column. Distillation
column (10)
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 (10) is
provided with an exit
pipe for product (11) and a tops pipe (12) which is in fluid flow
communication with
line (14) to liquid-phase separator (7).
In operation, in Figure 3, the reactor (2) is charged through feed pipe (1)
with a
feed stream containing fresh hydrogen fluoride and recycled hydrogen fluoride
from
line (8). The product from reactor (2) comprising HFC 227ea, hydrogen fluoride
and
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23-05-2001 GB 000001861
CA 02373437 2001-11-16
unconverted HFP, often in the form of a ternary azeotrope, travels through
product pipe
(14) to the liquid-phase separator (7). HFP is fed via feed line (13) and
product pipe
(14) to liquid-phase separator (7). The liquid-phase separator {7) is
typically operated at
0-20°C to afford better separation. In the liquid-phase separator (7),
an HF-rich phase
separates from the organics-rich phase. The HF-rich phase is returned via tops-
line (8) to
feed-pipe (1). The organics-rich phase flows via bottoms line (9) to
distillation column
(10). A stream comprising HFP and essentially all the hydrogen fluoride
content of the
stream entering distillation column (10) via line (9) is removed from the top
of
distillation column (10) via line (12) and returned to the liquid phase
separator (7) via
line ( 14). The product stream HFC 227ea is removed from the bottom of column
(10)
via exit pipe (11).
In the ternary diagram in Figure 4, compositions in the area of the figure
designated A phase-separa~namely compositions com hn,''syng 0.4-0.6 mole
greater than 0.4 mole HFP and less than 0.6 moleHFC 227ea.
The present invention is further illustrated by reference to the following
Examples.
Examples 1-4
These examples 1-4 illustrate the liquid-phase separation of HFP 227ea from HF
and the enhanced separation thereof in the presence of HFP.
In the Examples, HFC 227ea and HFP, where used, were added to HF in a 500
ml whitey bomb~cooled in liquid nitrogen. The whitey bomb was provided with a
double-dip arrangement such that the dip-pipes would sample from the middle of
each
phase. The mixture was allowed to warm to room temperature, agitated, allowed
to stand
for 2 hours and then analysed.
The HF phase was analysed for organics by transferring a portion of the HF
phase ( 1 Og) to a smaller whitey bomb containing water. It was allowed to
stand for 15
minutes then the headspace was analysed by G.C.
The organics phase was analysed for HF by bubbling a portion of the organics
phase through water scrubbers containing fresh de-ionised water and ice. The
water was
then analysed for fluoride.
The results are shown in the Table from which it can be seen that (a) a
mixture of
HFC 227ea and HF phase-separates such that an organic layer and an HF-rich
layer are
formed (Example 1 ) and (b) addition of HFP to the HFC 227ea/HF mixture
reduces the
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AMENDED SHEET
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WO 00/69797 PCT/GB00/01861
concentration of HF in the organic phase and significantly reduces the
concentration of
HFC 227ea in the HF phase (Examples 2-4).
Table
Example Compon- Mass %w/w mole %w/w %w/w %w/w
No. ents (g) fractionHF 227ea HFP in
in organicin HF phase
phase HF phase
1 HF 44.07 8.31 0.44 5.29
227ea 486 91.69 0.56 22.56
2 HF 39.74 7.43 0.4 3.14
227ea 410.46 76.76 0.49 8.98
HFP 84.54 15.81 0.11 2.07
3 HF 33.32 6.16 0.35 3.54
227ea 367 67.88 0.45 10.81
HFP 140.3 25.96 0.2 5.47
4 HF 30.06 5.56 0.32 0.33
227ea 312.7 57.86 0.4 9.35
HFP 198 36.62 0.28 6.21
30
9
