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FIELD OF THE INVENTION
A subject-matter of the invention is a process for the preparation of fluoroolefin
compounds. The invention relates more particularly to a process for the preparation of
hydrofluoropropenes.
TECHNOLOGICAL BACKGROUND
Hydrofluorocarbons (HFCs) and in particular hydrofluoroolefins (HFOs), such as
2,3,3,3-tetratluoro-1-propene (HF0-1234yf), are compounds known for their properties
of refrigerants and heat-exchange fluids, extinguishers, propellants, foaming agents,
blowing agents, gaseous dielectrics, monomer or polymerization medium, support
fluids, agents for abrasives, drying agents and fluids for energy production units.
Unlike CFCs and HCFCs, which are potentially dangerous to the ozone layer, HFOs do
not comprise chlorine and thus do not present a problem for the ozone layer.
1,2,3,3,3-Pentatluoropropene (HF0-122Sye) is a synthetic intermediate in the
manufacture of 2,3,3,3-tetrafluoro-1 ~propene (HF0-1234yf).
The majority of the processes for the manufacture of hydrofluoroolefins involve
a dehydrohalogenation reaction. Thus, the document WO 03/027051 describes a
process for the manufacture of fluoroolefins of formula CF3CY=CXnHp, in which X andY
each represent a hydrogen atom or a halogen atom chosen from fluorine, chlorine,
bromine or iodine and n and p are integers and can independently take the value zero,
1 or 2, provided that (n + p) = 2, which comprises bringing a compound of formula
CF3C(R1aR2b)C(R3,R4
d), with R1
, R2
, R3 and R4 independently representing a hydrogen
atom or a halogen atom chosen from fluorine, chlorine, bromine or iodine, provided
that at least one of Rl, R2
, R3 and R4 is a halogen atom and that at least one hydrogen
atom and one halogen atom are situated on adjacent carbon atoms, a and b being
able independently to take the value zero, 1 or 2, provided that (a+ b)= 2, and c and
d being able independently to take the value zero, 1, 2 or 3, provided that (c +d)= 3,
into contact with at least one alkali metal hydroxide in the presence of a phase transfer
catalyst.
This document teaches, in Example 2, that, in the absence of a phase transfer
catalyst, there is no reaction when 1,1,1,3,3-pentafluoropropane (HFC-245fa) is
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brought into contact with a 50% by weight aqueous potassium hydroxide (KOH)
solution at ambient temperature and under pressure for 24 hours.
In addition, this document teaches a reaction temperature of between -20°C
and 80°C.
The document WO 2008/075017 illustrates the dehydrofluorination reaction of
1,1,1,2,3,3-hexafluoropropane (HFC-236ea) to give 1,2,3,3,3-pentaftuoropropene
(HF0-1225ye) at 150°C in the presence of a 50% by weight aqueous KOH solution. In
the absence of a phase transfer catalyst, the conversion after 3 and a half hours is
57.8% and the selectivity for HF0-1225ye is 52.4 % (Test 1). In the presence of a
phase transfer catalyst, this conversion is achieved after only 2.5 hours and the
selectivity is virtually unchanged (Test 4). As indicated in Table 2 of this document, it is
necessary to use an organic solvent in order to increase the selectivity for HF0-1225ye.
WO 2007/056194 describes the preparation of HF0-1234yf by dehydrofluorination
of 1,1,1,2,3-pentafluoropropane (HFC-245eb) either with an aqueous KOH
solution or in the gas phase in the presence of a catalyst, in particular over a catalyst
based on nickel, carbon or a combination of these.
The document Knunyants et al., Journal of the USSR Academy of Sciences,
Chemistry Department, "Reactions of fluoro-olefins", Report 13, " Catalytic
hydrogenation of perfluoro-otefins", 1960, dearly describes various chemical reactions
on fluorinated compounds. This document describes the dehydrofluorination of
1,1,1,2,3,3-hexafluoropropane (236ea) by passing through a suspension of KOH
powder in dibutyl ether, to produce 1,2,3,3,3-pentafluoro-1-propene (HF0-1225ye)
with a yield of only 60%. This document also describes the dehydrofluorination of
1,1, 1,2,3-pentafluoropropane (HFC-24Seb) to give 2,3,3,3-tetrafluoro-1-propene (HF0-
1234yf) by passing into a suspension of KOH powder in dibutyl ether with a yield of
only 70%.
Furthermore, Figure 2 on page 51 of Part 2 of the nouveau traite de chimie
minerale [New Treatise on Inorganic Chemistry] by P. Pascal, Ed. 1963, shows the
appearance of the liquid/solid equilibria of the water and potassium hydroxide system
and the measurements are collated in the table on page 52.
The dehydrofluorination reactions as described above result, in addition to the
desired hydrofluoroolefin compound, in the formation of water and potassium fluoride.
Furthermore, the implementation of such a reaction continuously is not easy on the
industrial scale as at least three phases (gas, liquid and solid) are involved.
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The present invention provides a process for the continuous or semicontinuous
manufacture of a (hydro)fluoroolefin compound which makes it possible to overcome
the abovementioned disadvantages. A subject-matter of the present invention is thus a
process for the continuous or semicontinuous manufacture of a (hydro)fluoroolefin
compound comprising (i) bringing at least one compound comprising from three to six
carbon atoms, at least two fluorine atoms and at least one hydrogen atom, provided
that at least one hydrogen atom and one fluorine atom are situated on adjacent
carbon atoms, into contact with potassium hydroxide in an aqueous reaction medium
in a stirred reactor equipped with at least one inlet for the reactants and with at least
one outlet, to give the (hydro)fluoroolefin compound, which is separated from the
reaction medium in the gaseous form, and potassium fluoride, (ii) bringing the
potassium fluoride formed in (i) into contact in an aqueous medium with calcium
hydroxide in a second reactor, to give potassium hydroxide and to precipitate caldum
fluoride, (iii) separating the calcium fluoride precipitated in stage (ii) from the reaction
medium and (iv) optionally recycling the reaction medium to stage (i) after optional
adjustment of the concentration of potassium hydroxide, characterized in that the
potassium hydroxide represents, in the reaction medium of stage (ii), between 10 and
35% by weight, with respect to the weight of the water and potassium hydroxide
mixture of the medium.
The present invention thus makes it possible to obtain an advantageous
process as, on the one hand, potassium hydroxide is more reactive than calcium
hydroxide in the dehydrofluorination reaction and, on the other hand, the conversion
of the calcium hydroxide to give calcium fluoride, a by-product which can be recovered
in value, is high.
The Applicant Company has observed that the process according to the present
invention makes it possible to obtain a mean size at 50% by weight of the particle size
distribution of calcium fluoride crystals of greater than 10 ~-tm, indeed even of greater
than 20 1-1m and more particularly of between 20 and 60 )lm and thus to facilitate the
washing and filtration operations and the recycling of the potassium hydroxide.
The reaction medium of stage (i) is stirred so as to provide for dispersion of the
gas in the liquid medium.
The process according to the present invention preferably provides a
(hydro )fluoroolefin compound comprising three carbon atoms, advantageously a
(hydro)fluoroolefin compound represented by the formula (I)
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CF3CY=C:XnHp (I)
in which Y represents a hydrogen atom or a halogen atom chosen from fluorine,
chlorine, bromine or iodine, X represents a halogen atom chosen from fluorine,
chlorine, bromine or iodine, and n and p are integers and can independently take the
value zero, 1 or 2, provided that (n + p) = 2, by bringing a compound of formula
CF3CYRCR'XnHp, in which X, Y, nand p have the same meanings as in the formula (I)
and R represents a fluorine atom when R' represents a hydrogen atom or R represents
a hydrogen atom when R' represents a fluorine atom, into contact with potassium
hydroxide in stage (i).
The present invention is very particularly suited to the manufacture of a
compound of formula (Ia)
CFrCF=CHZ (Ia)
in which Z represents a hydrogen atom or a fluorine atom, starting from a compound
of formula CF3CFRCHR'Z in which Z has the same meanings as in the formula (Ia) and
R represents a fluorine atom when R' represents a hydrogen atom or R represents a
hydrogen atom when R' represents a fluorine atom.
Thus, 2,3,3,3-tetrafluoropropene can be obtained by dehydrofluorination of
1,1,1,2,3-pentafluoropropane with KOH and/or 1,2,3,3,3-pentafluoropropene can be
obtained by dehydrofluorination of 1,1,1,2,3,3-hexafluoropropane with KOH in stage
(i). The 1,2,3,3,3-pentafluoropropene can be in the form of the cis and/or trans
isomer.
The present invention can additionally be used for the manufacture of 1,3,3,3-
tetrafluoropropene by dehydrofluorination of 1,1,3,3,3-pentafluoropropane with KOH.
In stage (i) of the process according to the present invention, the potassium
hydroxide can represent between 20 and 75% by weight, with respect to the weight of
the water and KOH mixture present in the aqueous reaction medium, preferably
between 55 and 70%. According to the content, the potassium hydroxide can be in the
form of an aqueous solution or in the molten state.
Stage (i) is generally carried out at a temperature such that the water formed
during the dehydrofluorination reaction is removed, in all or in part, from the reaction
medium by entrainment of the gas stream comprising the (hydro)fluoroolefin
compound resulting from the stirred reactor. This temperature is preferably between
80 and 180°C, advantageously between 125 and 180°C and very particularly between
145 and 165°C.
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The dehydrofluorination reaction of stage (i) can be carried out at atmospheric
pressure but it is preferable to operate at a pressure greater than atmospheric
pressure. Advantageously, this pressure is between 1.1 and 2.5 bar.
The reaction of stage (ii) can be carried out in a stirred reactor or a fluidized
bed reactor by reacting calcium hydroxide, preferably in suspension in water, with the
potassium fluoride originating from stage (i). The reaction temperature can vary within
wide limits but, for economic reasons, it is preferably between 50 and 150°C,
advantageously between 70 and 120°C and more advantageously between 70 and
100°C.
When a calcium hydroxide suspension is used in stage (ii), the calcium
hydroxide represents between 2 and 40% by weight, with respect to the weight of the
suspension.
Advantageously, stage (ii) is fed with potassium fluoride via the reaction
medium originating from stage (i) comprising water, potassium hydroxide and
potassium fluoride. The potassium fluoride in stage (i) can be dissolved or in
suspension. The potassium fluoride preferably represents between 4 and 45% by
weight of the reaction medium from stage (i).
In the stage (ii), two mol of potassium fluoride react with one mol of calcium
hydroxide to give one mol of potassium fluoride and two mol of potassium hydroxide.
This generation of potassium hydroxide makes it possible to limit the optional need to
reconcentrate and thus reduces the addition of potassium hydroxide in the process.
It is possible to provide a stage of dilution of the reaction medium between
stage (i) and stage (ii).
The calcium fluoride precipitated in stage (ii) is separated from the reaction
medium, for example by filtration and/or settling. A settling stage can be provided prior
to the filtration. The calcium fluoride thus separated is subsequently washed with
water.
During the settling stage, it is possible to provide for the recycling of a portion
of the concentrated calcium fluoride suspension to stage (ii). Advantageously, the level
of calcium fluoride solids present in the reaction medium of stage (ii) is between 2 and
30% by weight.
After separation of the calcium fluoride, the reaction medium, with or without
aqueous liquors from washing the calcium fluoride, can be recycled to stage (i), after
optional adjustment of the potassium hydroxide content.
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It can be advantageous to use an inert gas in the dehydrofluorination stage.
The process according to the invention has the advantage of resulting in high
yields, even in the absence of phase transfer catalyst and/or organic solvent.
The present invention also comprises the combinations of the preferred forms,
whatever the embodiment.
EXPERIMENTAL PART
Example 1
1 kg of 50% by weight potassium hydroxide comprising 9% by weight of KF is
introduced into a reactor and heated to 100°C. 109 g of ca(OHh assaying 96% by
weight (major impurity being caco3) are subsequently added with stirring at 500
revolutions/min. After reacting for one hour, the suspension is withdrawn. The level of
solids is 3.5% by weight and the composition by weight of the solids is as follows:
caFz: 60%
ca(OH)z: 36%
caco3: 4%
Example 2
The operation is carried out as in Example 1, except that 1 kg of 25% by weight
potassium hydrroxide is introduced.
The composition by weight of the solids, after reacting for one hour, is as follows:
caF2: 95%
ca(OH)z: 1%
caco3: 4%.
Example3
A reactor maintained at 100°C and stirred at 500 rev/min is fed continuously with a
potassium hydroxide solution resulting from the dehydrotluorination stage and
assaying, after dilution, 28% by weight of potassium hydroxide and 6% by weight of
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KF. The Ca(OHh suspension feeding the reactor assays 20% by weight. The residence
time in the reactor is approximately l h.
The ability to be filtered of the suspension obtained after reaction is very good.
The level of solids of the suspension at the outlet of the reactor is 3.6% by weight.
The particle size of the calcium fluoride synthesized is 30 1Jm and its purity is greater
than 85% by weight.
Example4
Figure 1 gives the diagram of an embodiment of the present invention. A stirred
reactor (1), equipped with a heating/cooling device and a device for measuring the
temperature of the reaction medium, which comprises a water and KOH mixture in
which the KOH is present at 60% by weight in the water, is fed continuously with a
solution of molten KOH (2), in which the KOH is present at 65% by weight in the
water, and with 1,1,1,2,3,3-hexafluoropropane (3). The temperature is maintained at
150°C and the pressure in the reactor is 1.2 bar absolute. The gaseous products exit
from the reactor via an orifice (4) situated on the lid and the water present in the gas
stream is removed by condensation (13).
The material exiting (5) from the reactor (1) is diluted in line with water (6) in order to
obtain a KOH assay of 30%. This mixture is conveyed to the inlet of the reactor (7)
and thus provides for the feeding of the reactor (7) with potassium fluoride, which can
be in suspension in the aqueous medium. A suspension of 15% by weight of calcium
hydroxide in water is introduced into the reactor (7) via the route (8). The reactor (7)
is maintained at a temperature of between 70 and 80°(.
The outlet of the reactor (7) is connected to a filter (9), in order to separate the
calcium fluoride from the reaction medium and then to wash it with water (10); the
aqueous medium separated from the calcium fluoride is subsequently recycled to the
reactor (1) after adjustment of the KOH concentration. The aqueous liquors from
washing the calcium fluoride are recycled to the tank (16) for preparation of the
suspension of calcium hydroxide in water.
The molten KOH mixture feeding the reactor (1) is prepared by evaporation (removal
of water (15)) of a SO% by weight aqueous KOH solution (14) and of the aqueous
solution originating from the filter (9).
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At the outlet of the reactor (1), the degree of molar conversion of the 1,1,1,2,3,3-
hexafluoropropane is greater than 98%. The selectivity for 1,1,1,2,3-
pentafluoropropene is greater than 99%.
At the outlet of the reactor (7), the degree of molar conversion of the calcium
hydroxide is greater than 85%.
Example 5
The operation is carried out at Example 4, except that the reactor (1) is fed
continuously with 1,1,1,2,3-pentafluoropropane instead of 1,1,1,2,3,3-
hexafluoropropane.
The stirred reactor (1) comprises a water and KOH mixture in which the KOH is
present at 65% by weight in the water.
At the outlet of the reactor (1), the degree of molar conversion of the 1,1,1,2,3,pentafluoropropane
is greater than 98%. The selectivity for 1,1,1,2-tetrafluoropropene
is greater than 99%.
Example 6
A reactor maintained at 80°C and stirred at 500 rev/min is fed continuously with a
potassium hydroxide solution resulting from the dehydrofluorination stage and
assaying, after dilution, 32.8% by weight of potassium hydroxide and 9.7% by weight
of KF. The ca(OHh suspension feeding the reactor assays 15% by weight. The
residence time in the reactor is approximately 1 h.
The ability to be filtered of the suspension obtained after reaction is very good.
The level of solids of the suspension at the outlet of the reactor is 3.6% by weight.
The particle size of the calcium fluoride synthesized is 30 !Jm and its purity is greater
than 85% by weight.

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We Claim:
1. Process for the continuous or semicontinuous manufacture of a
(hydro)fluoroolefin compound comprising (i) bringing at least one compound
comprising from three to six carbon atoms, at least two fluorine atoms and at least
one hydrogen atom, provided that at least one hydrogen atom and one fluorine atom
are situated on adjacent carbon atoms, into contact with potassium hydroxide in an
aqueous reaction medium in a stirred reactor equipped with at least one inlet for the
reactants and with at least one outlet, to give the (hydro )fluoroolefin compound, which
is separated from the reaction medium in the gaseous form, and potassium fluoride,
(ii) bringing the potassium fluoride formed in (i) into contact in an aqueous medium
with calcium hydroxide in a second reactor, to give potassium hydroxide and to
precipitate calcium fluoride, (iii) separating the calcium fluoride pr~ipitated in stage
(ii) from the reaction medium and (iv) optionally recycling the reaction medium to
stage (i) after optional adjustment of the concentration of potassium hydroxide,
characterized in that the potassium hydroxide represents, in the reaction medium of
stage (ii), between 10 and 35% by weight, with respect to the weight of the water and
potassium hydroxide mixture of the medium.
2. Process according to Claim 1, characterized in that the (hydro)fluoroolefin
compound of formula (I)
CF3CY =CX.,Hp (I)
in which Y represents a hydrogen atom or a halogen atom chosen from fluorine,
chlorine, bromine or iodine, X represents a halogen atom chosen from fluorine,
chlorine, bromine or iodine, and n and p are integers and can independently take the
value zero, 1 or 2, provided that (n + p) = 2, is obtained by bringing a compound of
formula CF3CYRCR'XnHp, in which X, Y, n and p have the same meanings as in the
formula (I) and R represents a fluorine atom when R' represents a hydrogen atom or R
represents a hydrogen atom when R' represents a fluorine atom, into contact with
potassium hydroxide in stage (i).
3. Process according to Claim 1, characterized in that the (hydro)fluorooletin
compound is of formula (Ia)
CFrCF=CHZ (Ia)
1l
in which Z represents a hydrogen atom or a fluorine atom, comprises bringing a
compound of formula CF3CFRCHR'Z, in which Z has the same meanings as in the
formula {Ia) and R represents a fluorine atom when R' represents a hydrogen atom or
R represents a hydrogen atom when R' represents a fluorine atom, into contact with
potassium hydroxide in stage (i).
4. Process according to any one of the preceding claims, characterized in that
2,3,3,3-tetrafluoropropene is obtained by bringing 1,1,1,2,3-pentafluoropropane into
contact with potassium hydroxide and/or 1,2,3,3,3-pentafluoropropene is obtained by
bringing 1,1,1,2,3,3-hexafluoropropane into contact with potassium hydroxide in stage
(i).
5. Process according to any one of the preceding claims, characterized in that the
potassium hydroxide can represent between 20 and 75% by weight, with respect to
the weight of the water and KOH mixture present in the aqueous reaction medium of
stage (i), preferably between 55 and 70% by weight.
6. Process according to any one of the preceding claims, characterized in that the
temperature at which stage (i) is carried out is between 80 and 180°C, preferably
between 125 and 180°C and advantageously between 145 and 165°C.
7. Process according to any one of the preceding claims, characterized in that the
temperature of stage (ii) is between 50 and 150°C, preferably between 70 and l20°C
and advantageously between 70 and 100°C.
8. Process according to any one of the preceding claims, characterized in that
stage (ii) is fed with potassium fluoride via the reaction medium originating from stage
(i).
9. Process according to any one of the preceding claims, characterized in that the
potassium fluoride represents between 4 and 45% by weight of the reaction medium
from stage (i).
10. Process according to Claim 8, characterized in that water is added to the
reaction medium of stage (ii).
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11. Process according to any one of the preceding claims, characterized in that the
calcium fluoride in stage (iii) is filtered off after an optional settling stage.
12. Process according to Claim 11, characterized in that, during settling, a portion
of the concentrated calcium fluoride suspension is recycled to stage (ii).
Dated this 22"d day of December, 2011.