Note: Descriptions are shown in the official language in which they were submitted.
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Preparation of halogen and hydrogen containing alkenes over metal
fluoride catalysts
A transformation of saturated halogenated, especially fluorinated C-2, C-3,
C-4 and C-5 alkanes into haloolefines, especially fluoroolefines, by
dehydrohalogenation, especially dehydrofluorination, is of industrial as well
as
of ecological importance. Chloroolefines and fluoroolefines are intermediates
in
chemical synthesis. Trifluoroethylene, for example, can be polymerized.
Fluoropropenes, for example, tetrafluoropropene and pentafluoropropene, are
also suitable as intermediates in chemical synthesis. Further, the isomers of
tetrafluoropropene and the isomers of pentafluoropropene, optionally in
admixture with other compounds or additives, can be applied as blowing agent
for preparation of plastic foams, as fire extinguishing agents or as
refrigerants,
for example, in mobile air conditioning ("MAC"). US patent 7,091,388
discloses the preparation of pentafluoropropene by treating
chloropentafluoropropane or hexafluoropropane with caustic or thermally over
supported transition metal halides or oxides or bulk transition metal oxides.
According to the examples disclosed therein, CF3-CH=CF2 (HFC-1225zc) is
produced from 1,1,3,3,3-pentafluoro-l-chloropropane (HFC-235fa) or
1,1,1,3,3,3-hexafluoropropane (HFC-245fa). WO 2004/096737 describes that
fluorobutenes and fluorobutadienes are suitable as monomers, as building
blocks
and as starting material for hydrofluorocarbons. This international patent
application describes that specific butenes and butadienes can be prepared
from
1, 1, 1,3,3 -pentafluorobutane by thermal, basic or catalytic
dehydrofluorination.
Titanium, manganese, chromium, iron, cobalt, nickel, copper, zirconium,
molybdenum, niobium, ruthenium, rhodium, palladium, silver, hafnium,
tantalum, tungsten, rhenium, iridium, platinum and antimony are mentioned as
suitable catalysts.
It is the objective of the present invention to provide a technically feasible
process for the preparation of fluoroalkenes. It is another object of the
present
invention to provide a supported catalyst suitable for the process of the
present
invention. These objectives and other objectives are achieved by the present
invention. In its broadest embodiment, the process of the present invention
provides for the preparation of halogenated alkenes whereby a halogenated
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alkane with at least one hydrogen atom is dehydrohalogenated in the presence
of
X-ray amorphous high surface metal fluoride or X-ray amorphous or weakly
crystalline metal oxide fluoride wherein the metal is selected from the 2, 3
or 4 main group or any subgroup of the periodic system of elements.
In one embodiment, the catalyst is a full catalyst. In another embodiment,
the catalyst is carried on a support.
Lewis-acidic metal fluorides are preferred, especially aluminium fluorides,
chromium fluorides and iron fluorides. Aluminium fluoride and aluminium
oxyfluoride are preferred as catalyst. Aluminium fluoride is especially
preferred
as catalyst (if desired, carried on a support).
In the context of the present invention, the terms "amorphous" and "X-ray
amorphous" are interchangeable. The metal fluorides have certain novel
characteristics when compared with fluorides of the state of the art. They
preferably have an active surface of about 100 - 300 rri /g (measured with N2,
e.g. in a micromeritics ASAP 2001). They are strong Lewis acids. They are
essentially free of Cl. The amorphous metal fluoride is X-ray amorphous. The
term "X-ray amorphous" denotes that the microcrystalline domains of the solid
matter, i.e. the amorphous metal fluoride, have a size of less than 20 nm.
They
have a mesoporous surface, as revealed by REM (Reflection Electron
Microscopy). These features especially apply to amorphous aluminium fluoride.
The amorphous aluminium fluoride has a strongly distorted structure of the
A1F3
octahedron. These disorders are responsible for the X-ray amorphous condition
of the solid matter. The quadrupol coupling constant is about 1.5 MHz. In the
IR spectrum, rather only a single very broad band (v3 of Al-F at 667 crri 1)
is
observed as can be allocated to the amorphous rather the crystalline
structure.
The increased Lewis acidity can be demonstrated by pyridine absorption and
NH3-TPD (NH3 temperature programmed desorption). The X-ray amorphous
catalysts, especially A1F3, have the advantage that they are not hygroscopic.
In the following, reference is made to the dehydrohalogenation process of
the present invention. It is clear for the expert that the description thereof
concerns the use of the above mentioned full catalyst as well as the above
mentioned supported catalyst.
The terms "hydrofluoroalkanes" and "hydrofluoroalkenes" denote
molecules which consist of fluorine, hydrogen and carbon. The terms
"chloroalkanes" and "chloroalkenes" denote compounds which consist of
chlorine and carbon, the terms "hydrochloroalkanes" and "hydrochloroalkenes"
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denote compounds which consist of chlorine, hydrogen and carbon. The terms
"hydrochlorofluoroalkanes" and "hydrochlorofluoroalkenes" denotes compounds
which consist of chlorine, fluorine, hydrogen and carbon. The terms
"chlorofluoroalkanes" and "chlorofluoroalkenes" denote compounds consisting
of chlorine, fluorine, and carbon. The term "perfluoroalkenes" denotes
compounds consisting of fluorine and carbon. This scheme for alkene
compounds analogously applies to alkadiene compounds.
For example, chlorinated alkenes or hydrochloroalkenes can be produced
from hydrochloroalkanes. Chlorofluoroalkenes or hydrochlorofluoroalkenes can
be produced from hydrochlorofluoroalkanes, and fluoroalkenes or
hydrofluoroalkenes or fluoroalkenes can be produced from hydrofluoroalkanes
or hydrofluorochloroalkanes with 1 chlorine atom. It is clear for the expert
that
hydrofluoroalkanes can produce fluoroalkenes (i.e., perfluoroalkenes) if only
one
hydrogen atom is present which is split off in the form of HF, or if two
hydrogen
atoms are split off as HF ; in the latter case, an alkadiene is produced. If
the
hydrofluoroalkane starting material has more than one hydrogen atom, then one
hydrogen atom is split off as HF, the other hydrogen atom or hydrogen atoms
remain in the molecule, and thus, a hydrofluoroalkene is produced. Preferably,
the alkane starting material (and thus, also the produced alkene) has 2 to
5 carbon atoms. Preferably, the number of chlorine atoms and/or fluorine atoms
in the halogenated alkane is equal to or higher than the number of hydrogen
atoms, provided at least one hydrogen atom is comprised. Preferably,
hydrochlorofluoroalkanes with one chlorine atom or more preferably
hydrofluoroalkanes are applied as starting material, and consequently,
hydrofluoroalkenes or fluoroalkenes are produced by dehydrofluorination or
dehydrochlorination, respectively. Especially preferably, a hydrofluoroalkane
is
transformed to a hydrofluoroalkene, a fluoroalkene, a hydrofluoroalkadiene or
a
fluoroalkadiene. In view of this preferred embodiment, the invention will be
described in detail.
The preferred process of the present invention provides for the preparation
of fluorinated alkenes and comprises a step of dehydrofluorination of a
hydrofluoroalkane with at least 1 hydrogen atom in the presence of an X-ray
amorphous high surface aluminium fluoride catalyst or in the presence of an
X-ray amorphous high surface aluminium fluoride catalyst carried on a support.
According to a preferred embodiment, fluorinated alkenes with 2 to
5 carbon atoms are produced from alkanes which have one hydrogen atom and
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one fluorine atom more than the produced alkene. According to another
preferred embodiment, fluorinated alkadienes are produced from alkanes which
have two hydrogen atoms and two fluorine atoms more than the fluorinated
alkadiene. The terms "fluorinated alkenes" and "fluorinated alkadienes" denote
compounds which consist of fluorine and carbon and which optionally comprise
also 1 or more hydrogen atoms. Principally, fluorinated alkanes can be applied
as starting compounds which comprise at least one fluorine atom ; or
hydrochlorofluoroalkanes with 1 chlorine atom and at least one fluorine atom ;
or, if fluorinated alkadienes are to be produced, hydrochlorofluoroalkanes
with 1
or 2 chlorine atoms and 2 hydrogen atoms. If an alkadiene is produced, then,
depending on the starting material, 2 HC1 molecules, 2 HF molecules or 1
molecule of each are split off. Preferably, fluorinated alkanes are applied as
starting compounds wherein the number of fluorine atoms is equal to or higher
than the number of hydrogen atoms. For example, cis- and
trans-1,1,1,2,4,4,5,5,5-nonafluoropentene-2, cis- and trans-1,1,1,3,4,4,5,5,5-
nonafluoropentene-2 can be prepared from 1, 1, 1,2,3,4,4,5,5,5 -
decafluoropentane.
Preferably, perfluoroalkenes or perfluoroalkadienes with 2 to 4 carbon
atoms are produced. Very preferably, hydrofluoroalkenes or
hydrofluoroalkadienes with 2 to 4 carbon atoms are produced.
According to one preferred embodiment, alkenes with 2 or 3 carbon atoms
are prepared. For example, tetrafluoropropenes can be prepared by
dehydrofluorination of a pentafluoropropane. Especially preferably,
pentafluoropropenes are prepared by dehydrofluorination of hexafluoropropanes.
Especially preferably, HFC-1225ye is prepared by dehydrofluorination of
1,1,1,2,3,3-hexafluoropropane or 1,1,1,3,3,3-hexafluoropropane ; or
trifluoroethene is prepared by dehydro fluorination of 1, 1, 1,2-
tetrafluoroethane.
The dehydro fluorination reaction takes place very selectively - also in view
of
stereochemistry - and in high yields. The temperature at which
dehydrochlorination or dehydrofluorination occurs depends from the respective
starting compound and if it concerns a dehydrochlorination or a
dehydrofluorination. Generally, the reaction temperature is equal to or higher
than 50 C, preferably equal to or higher than 150 C. The reaction can be
performed at even lower temperature, but in some cases, the speed of reaction
may be considered to be too low. Generally, the reaction is performed at a
temperature equal to or lower than 500 C, preferably equal to or lower than
450 C, and very preferably equal to or lower than 420 C. The catalyst is very
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active for extended periods of time when the reaction temperature is equal to
or
lower than 400 C. The result of the dehydrochlorination or dehydrofluorination
is very good at temperatures e.g. above 400 C. The long-term performance of
the catalyst is especially good if it is operated at temperatures equal to or
below 400 C.
For dehydrofluorination, the reaction temperature is preferably equal to or
higher than 200 C. The speed of reaction can be accelerated if the reaction
temperature is equal to or higher than 250 C. Often, performing the reaction
in a
range of 300 C to 400 C allows a high reaction speed with high conversion. A
fast reaction and high conversion are observed even if the dehydrofluorination
temperature is equal to or higher than 400 C. It may be equal to or lower
than 500 C.
In some cases, the balance between high reaction speed and high
selectivity may favour operation at relatively low reaction temperature. For
example, as demonstrated in an example, the dehydrofluorination of
1,1,1,2,3,3-hexafluoropropane, if performed at a temperature of 250 C, yields
selectively the (Z) isomer of 1,1,1õ2,3-pentafluoropropene which is the
preferred
isomer when applied as such, for example, as refrigerant, solvent, fire
extinguishant or foam blowing agent because it is the more stable one. On the
other hand, if obtaining mixtures of the (E) and (Z) isomers is acceptable, a
higher reaction temperature will be selected because of the higher reaction
speed.
Compounds which can be produced are for example :
= fluoroethene from 1, 1 -difluoroethane
= 1,1,2-trifluoroethene from 1,1,2,2-tetrafluoroethane or
1, 1, 1,2-tetrafluoroethane
= 1,1,3,3,3-pentafluoropropene (HFC-1225zc) from
1,1,1,3,3,3-hexafluoropropane
= 1,2,3,3,3-pentafluoropropene from 1,1,1,2,3,3-hexafluoropropane
= Cis- and trans-1,2,3,3-tetrafluoropropene and 1,1,2,3-tetrafluoropropene
from
1,1,2,2,3-pentafluoropropane
= Cis- and trans-1,3,3,3-tetrafluoropropene and 1,1,3,3-tetrafluoropropene
from
1,1,1,3,3-pentafluoropropane
= 2,3,3,3-tetrafluoropropene from 1,1,1,2,2-pentafluoropropane
= 1,1,2-trifluoroethene from 1,1,2-trifluoro-2-chloroethane
= 1,1,1,3,3-pentafluoropropene from 1,1,1,3,3-pentafluoro-3-chloropropane or
1,1,1,3,3-pentafluoro-2-chloropropane.
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According to another preferred embodiment, hydrofluoroalkanes with
4 carbon atoms and 1 to 9 fluorine atoms are dehydrofluorinated. For
example, 1,1,2,3,3,4,4-heptafluorobutene can be produced from
1,1,2,2,3,3,4,4-octafluorobutane. It is preferred to treat C4
hydrofluoroalkanes with 4, 5 or 6 fluorine atoms and 6, 5 or 4 hydrogen
atoms, respectively, in the dehydrofluorination reaction of the present
invention.
Especially preferably in this embodiment, 1,1,1,3,3-pentafluorobutane is
dehydrofluorinated. In a lower temperature range, predominantly one molecule
of HF splits off from one molecule 1,1,1,3,3-pentafluorobutane. At higher
temperatures, 2 molecules split off, and besides the butenes, also
1,1,3-trifluorobutadiene is formed.
To produce tetrafluorobutenes from 1,1,1,3,3-pentafluorobutane, the
temperature at dehydrofluorination is equal to or higher than 50 C, preferably
equal to or higher than 100 C, especially preferably equal to or higher than
180 C. Preferably, it is equal to or lower than 420 C. The temperature can
even
be higher, up to 500 C. If it is desired to produce the C4F4H4 with low C4F3H3
formation, the temperature is preferably equal to or lower than 260 C. To
produce C4F4H4 with a low content of the isomer with the lowest retention time
in the gas chromatogram, the reaction is preferably performed at a temperature
equal to or higher than 400 C. To produce trifluorobutadiene (often besides
tetrafluorobutenes), the temperature is preferably equal to or higher than 260
C,
preferably equal to or higher than 350 C. Often, the temperature is here equal
to
or less than 420 C. If, caused by too high temperatures, an undesired catalyst
deactivation is observed, the temperature is reduced respectively.
In the dehydrofluorination reaction of 1, 1, 1,3,3-pentafluorobutane, isomers
are produced, namely 2,4,4,4-tetrafluoro-l-butene and (E) and (Z)
1,1,1,3-tetrafluoro-2-butenes. They have different boiling points and can be
separated by distillation. If two molecules of HF are split off,
1,1,3-trifluorobutadiene is formed.
The expert is aware that the dehydro fluorination reaction can be performed
within the temperature ranges given above with good yield. He is aware that
often, he can perform the reaction at even lower temperatures, but with lower
yield. He is also aware that he can perform the reaction at higher
temperatures
than those given above ; often, the yield per time unit is better, but
sometimes the
selectivity may become lower, or, if 1,1,1,3,3-pentafluorobutane is
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dehydrofluorinated, the molar ratio of butane products may vary.
Trifluorobutadiene is produced in good yield at temperatures equal to or
higher
than 350 C, but it forms even at lower temperatures.
If one observes diminishing catalyst activity, e.g. after long reaction
periods, or if the reaction temperature was selected too high, a regeneration
of
the catalyst is possible. Oxidizing gases can be passed at elevated
temperatures
through the reactor, e.g. air or oxygen. As is described below, the catalytic
activity can be extended by passing a hydrofluorocarbon/nitrogen (or inert
gas)
mixture through the reactor.
The reaction can be performed batch wise or continuously. It is preferred
to operate in the gas phase, especially continuously.
If desired, the halogenated hydrocarbon can be diluted before the
dehydrohalogenation reaction with an inert gas, for example, nitrogen, or a
noble
gas, for example, argon. In this case, the halogenated hydrocarbon preferably
is
present in the gas mixture with inert gas in an amount of equal to or more
than 10 vol.-%. Preferably, it is present in an amount of equal to or less
than 75 vol.-%, more preferably in an amount of equal to or less than 50 vol.-
%,
and especially preferably equal to or less than 35 vol.- %. The productivity
of
the catalyst was observed to be higher when using inert gas (nitrogen for
example).
In another aspect of the present invention mixtures comprising or
consisting of nitrogen and a hydrofluorocarbon with 2 to 5 carbon atoms in a
molar ratio of N2:hydrofluorocarbon of (2 - 9):1, preferably of (3 - 6):l are
passed over the catalyst. Mixtures comprising or consisting of nitrogen and a
hydrofluorocarbon with 2 to 5 carbon atoms in a molar ratio of
N2:hydrofluorocarbon of (3 - 5):l are especially preferred. Especially
preferred
are mixtures comprising or consisting of Nz and a C3 or C4 hydrofluorocarbon
in
a molar ratio of (2 - 9):1, preferably (3 - 6):1, more preferably (3-5):1.
Most
preferred are mixtures consisting of Nz and pentafluoropropane,
hexafluoropropane, pentafluorobutane or hexafluorobutane. In this embodiment,
the hydrofluorocarbon is especially preferably 1, 1, 1,2,3,3 -
hexafluoropropane,
1,1,1,3,3,3-hexafluoropropane, 1,1,1,2,3,3-hexafluoropropane or, most
preferred,
1,1,1,3,3-pentafluorobutane. Mixtures consisting of nitrogen and
1, 1, 1,3,3 -pentafluorobutane in a molar ratio of Nz: l, l, l,3,3-
pentafluorobutane of
(2 - 9):1, preferably (3 - 6):1, most preferably 3 - 5):l are especially
preferred.
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Without intending to limit the invention to this explanation, it is assumed
that the surface of the catalyst, by the sweep of inert gas, is kept
relatively free
from molecules, e.g. HF, which may block or otherwise influence the acidic
centres of the catalyst.
The resulting product gas mixture comprises the produced haloalkene,
hydrogen halide, e.g. HC1 or HF, and often also starting compound or
haloalkadiene. If the starting compound was entered into the reaction in
diluted
form, also the diluent gas will be contained in the product gas mixture. The
work up can be performed in a known manner. For example, the product gas
mixture can be passed through a wet washer (a washer operated with water,
optionally containing a base, for example, sodium hydroxide, sodium carbonate,
sodium hydrogen carbonate, calcium hydroxide, or calcium carbonate, or even
an amine) and/or a dry agent, for example, KF or NaF to remove HF or HC1.
The gases passing the washer can be condensed in a cooled trap to condense
product and starting compound. They can be separated by known technique, for
example, pressure distillation or deep temperature distillation.
Also in some other reactions, for example, the dehydrofluorination of
1, 1, 1,2,3,3 -hexafluoropropane or 1, 1, 1,3,3 -pentafluorobutane, the
product may
be obtained in the form of isomers. No separation of the isomers is needed if
an
isomer mixture suits the intended use. If a separation of the isomers appears
desirable, this can often be achieved by methods known in the art. Sometimes,
these isomers can be separated by distillation. In other cases, the undesired
isomer can be converted into the other isomer. For example, in case of the
dehydrofluorination of 1, 1, 1,2,3,3 -hexafluoropropane, a mixture of (Z) and
(E)
isomers of HFC-1225ye is obtained. While this (E)/(Z) mixture can be applied
as refrigerant, as solvent or for any other purposes, the (Z) isomer appears
to be
the preferred one because it is more stable than the (E) isomer. If desired,
the (E)
isomer can be converted to the (Z) isomer as described by D. J. Burton,
T. D. Spawn, P. L. Heinze, A. R. Bailey and S. Shin-Ya in J. Fluorine
Chemistry 44 (1989), pages 167 to 174 by contacting it with SbFs.
According to one preferred aspect of the present invention, a process is
provided which comprises the steps of preparing mixtures of the (E) isomer and
the (Z) isomer of CF3-CF=CHF (HFC-1225ye) according to the invention and a
subsequent step of treating these mixtures with SbFs or with UV light to
convert
the (E) isomer into the (Z) isomer. In this way, the (Z) isomer of HFC-1225ye
is
provided which is essentially free of the (E) isomer without the need for
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distillation or other separation processes. The term "essentially" denotes
preferably that the (Z) isomer of HFC-1225ye comprises equal to or less
than 5 % by weight, preferably, equal to or less than 3 % by weight of the (E)
isomer.
Recycling of unreacted starting material or unwanted reaction product to
the dehydrofluorination reactor is possible. Often, for example, when
1, 1, 1,3,3 -pentafluorobutane is dehydrofluorinated, several reaction
products are
obtained, especially, tetrafluorobutenes and trifluorobutadiene. If
trifluoributadiene is the desired product, the fluorobutenes formed can be
recycled to the dehydrofluorination reactor.
In the following, the synthesis of the catalyst is described.
The X-ray amorphous high surface metal fluoride, which preferably is
aluminium fluoride ("HS-A1F3" ; it is one of the strongest solid Lewis acids
at
all) can be applied as full catalyst (or "bulk" catalyst), or in the form of a
coating
on a support. In the following, the full or bulk catalyst, in view of the
preferred
metal fluoride, HS-A1F3, is described in detail.
The synthesis of the high surface area aluminium fluoride (HS-A1F3), as
well as of other high surface are metal fluorides, can be performed as
described
in US 2006/0052649 or EP 1440939 Al (method for the preparation of
amorphous metal fluorides), and EP 1666411 Al (method for the preparation of
X-ray amorphous or weakly crystalline metal oxide fluorides and new uses
thereof). Amorphous metal fluoride is preferred. It can be prepared as
described
in EP 1440939 Al. Amorphous high surface area aluminium fluoride (or other
high surface area metal fluorides) is prepared by a method comprising the
steps
of
a) providing a precursor, whereby the precursor comprises a structure having a
formula of MX+F(X_s)_yByLd ; and
b) reacting the precursor with a fluorinating agent generating the amorphous
metal fluoride having a formula of MX+FX_s) ;
whereby M is a metal of the 2"a, 3ra or 4h main group or any metal from a
sub-group of the periodic system of the elements, preferably aluminium ; B is
a
co-ordinately bound group ; x is in case of aluminium 3 ; y is any integer
betweenl and3;8is0to0.1 ;andx-8>y.
B is preferably an alkoxide, enolate or carboxylic acid group, more
preferably an alkoxide of the formula -O-C,Hzc+i wherein c is any integer from
1
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to 6 ; L is a solvent, preferably an anhydrous organic solvent selected from
the
group comprising alcohols, ethers, ketones, alkanes, aromatics ; and d is < 1.
According to EP 1440939 Al, the precursor is obtained by reacting MX+BX,
wherein B is preferably an alkoxide, if the metal M is aluminium, B is more
preferably propoxide, dissolved or suspended in an organic solvent L, with 2
to 4 equivalents, preferably 3 equivalents, anhydrous HF, preferably dissolved
in
an organic solvent L', whereby L' can be any of the solvents L and also L' can
be equal to L ; followed by removing excessive solvents under vacuum at
temperatures equal to or less than 350 C, preferably equal to or less than 200
C,
still more preferably equal to or less than 100 C ; providing a precursor as
defined above.
The preparation of the precursor is preferably performed in a water free
solvent, preferably selected from the group consisting of alcohols, ethers,
ketones, alkanes, petroleum ether, formic acid, acetic acid or propionic acid.
Alcohols of formula C,H2c+1OH with c = 1 to 6, especially 1 to 3, are
preferred.
The precursor obtained thereby, in a second step, is further fluorinated,
"activated", whereby gaseous fluorinating agents are used at elevated
temperatures, preferably hydrofluorocarbons or hydrofluorochlorocarbons,
especially CHC1F2 or, still more preferably, CH2F2 at temperatures between up
to
350 C, or gaseous HF at temperatures from 50 C up to 300 C, preferably at
75 C up to 150 C. The fluorinating agent is preferably admixed with an inert
gas such as nitrogen or argon, whereby up to 95 % by volume inert gas can be
used ; providing an amorphous metal fluoride as defined above, whereby in case
of activation with HF the obtained metal fluoride, specifically if the metal
is
aluminium, can contain adsorbed HF, which can be removed by subsequent
exposure to an inert gas stream at temperatures up to 250 C.
In a preferred embodiment, the amorphous high surface metal fluoride
consists essentially of aluminium fluoride. The term "essentially" denotes
preferably that the content of other amorphous metal fluorides is equal to or
less
than 3 % by weight, still more preferably equal to or less than 2 % by weight.
EP 1440939 Al discloses another embodiment wherein MX+F(X_s)_yBy is
used as starting material, and which is not coordinated with a solvent.
In another embodiment, if desired, the aluminium fluoride can be doped
with metal fluorides of zinc, tin, copper, chromium, vanadium, iron, or
magnesium.
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The amorphous metal fluoride obtained has an extraordinary high surface
area, preferably in the range of 100 to 300 rri /g, as measured according to
the
BET method using N2 (see [0091] of US 2006/052649 Al for details, e.g.
suitable apparatus for determination of the specific surface) and in case of
Lewis
acidic metal ions an unusual high Lewis acidity, which in case of aluminium
fluoride, HS-A1F3, equals that of SbFs.
Details and examples for the preparation of high surface area metal
fluorides are given in EP 1440939 Al.
Amorphous aluminium fluoride is the preferred metal fluoride. The
process of the present invention yields the dehydrohalogenated products in
good
yield and good selectivity.
The amorphous metal fluoride, especially A1F3, carried on a support, is
highly suitable for application in the above described process of the present
invention.
High surface X-ray amorphous metal fluoride on a support, preferably with
the exception of MgFz as support, is novel and another aspect of the present
invention. The supported highly Lewis acidic catalysts the catalytic activity
of
which for the tested dehydro fluorination reactions are similar to that of the
known bulk catalyst (which is not concerned in the context of the present
invention). In principle, the metal can be selected from the 2"a, 3ra or 4~'
group
or the sub groups of the periodic system of the elements. Of course, if
desired,
the supported catalyst may comprise mixed amorphous metal fluorides.
Preferred amorphous metal fluorides are those of Al, Cr, Fe, V, Ga and Mg.
Amorphous aluminium fluoride is the preferred metal fluoride also for the
supported catalysts. Preferably, a support is selected which has a suitably
shaped
form, is chemically and thermally stable under the conditions of catalyst
synthesis and under reaction conditions of catalyst use, mechanically stable,
not
deteriorating the performance of the catalyst, not interfering with the
catalysed
reaction, and enabling anchoring of HS-A1F3. Any support which meets these
requirements can be used. For example, oxides, fluorides and oxifluorides of
aluminium or of transition metals are very suitable. Usually, these are
present in
crystalline form. Activated carbon can also be applied ; in a preferred
embodiment, aluminium oxide or aluminium fluoride is used as support ; in a
more preferred embodiment aluminium oxide is used, and in an even more
preferred embodiment y-A1203 is used as support. In this case, the supported
metal fluoride is high surface metal fluoride on y-A1203.
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Very preferably, the supported amorphous metal fluoride catalyst is
HS-A1F3 on a support, e.g., HS-A1F3 on y-A1203. If desired, the aluminium
fluoride can be doped with one or more other metal fluorides, for example, the
fluorides of zinc, tin, copper, iron, chromium, vanadium or magnesium. Such
doped supported catalysts can be prepared by adding hydrolysable metal
compounds, for example, the metal alkoxides to the hydrolysable aluminium
compound.
Preferably, the total amount of coated amorphous metal fluoride, especially
of A1F3 in the supported catalyst is equal to or greater than 3 % by weight,
more
preferably equal to or more than 4 % by weight. Preferably, the content of
aluminium fluoride in the supported catalyst is equal to or less than 30 % by
weight, more preferably equal to or less than 20 % by weight. In some
applications, the content can be equal to or less than 10 % by weight. A range
with good results, e.g. in dehydrofluorination reactions, is between 4 and 20
%
by weight. A range of 4 to 8 % by weight also gives good results.
In the following, the preparation of amorphous metal fluorides, especially
amorphous aluminium fluoride (HS-A1F3), supported on a carrier, will be
described. The terms "carrier" and "support" are interchangeable in the frame
of
the present invention.
The synthesis of the high surface area aluminium fluoride (HS-A1F3),
coating, as well as coatings of other high surface are metal fluorides, can be
performed analogously as described in US 2006/0052649 or EP 1440939 Al
(method for the preparation of amorphous metal fluorides), and EP 1666411 Al
(method for the preparation of X-ray amorphous or weakly crystalline metal
oxide fluorides and new uses thereof). A coating of amorphous metal fluoride
as
described in EP 1440939 Al is preferred. In a preferred embodiment, the
amorphous high surface metal fluoride consists essentially of aluminium
fluoride. The term "essentially" denotes preferably that the content of other
amorphous metal fluorides in the coating is equal to or less than 3 % by
weight,
still more preferably equal to or less than 2 % by weight.
The synthesis of supported high surface area metal fluoride on a support,
preferably aluminium fluoride on a support (HS-A1F3/support) follows basically
the synthesis route outlined for HS-A1F3 in EP 1440939 Al extended for a step
of anchoring to a suitable support at an appropriate stage of HS-A1F3
synthesis.
It is known from EP 1666411 Al that the Lewis acidity of amorphous high
surface area aluminium fluoride becomes reduced upon partial substitution of
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fluoride by oxide, consequently, if formation of oxyfluoride is to be avoided,
reducing adsorbed water and/or inherent OH-groups of the support by thermal
pre-treatment preserves the Lewis acidity, i.e. the catalytic performance of
the
anchored HS-A1F3, i.e. of the final catalyst. Therefore, the support, e.g. y-
A1203,
is preferably heated prior to the coating procedure. Heating is preferably
performed for equal to or less than 48 hours, preferably equal to or less than
12 hours, advantageously at temperatures which do not result in undesired
transformation of the support. For example, it is avoided to transform y-A1203
into (x-A1z03 (which can be determined by X-ray powder diffraction). For
example, y-A1203 can be heated to temperatures between 400 C and 900 C.
Preferably, it is heated to a temperature equal to or higher than 600 C.
Preferably, it is heated to a temperature equal to or lower than 900 C in air
and
subsequently cooled down to room temperature under exclusion of moisture.
According to this aspect of the present invention, amorphous high surface
area metal fluoride is prepared by a method comprising the steps of
a) providing a precursor coated on a support, whereby the precursor comprises
a
structure having a formula of MX+F(X_s)_yByLd ; and
b) reacting the precursor with a fluorinating agent generating the amorphous
metal fluoride having a formula of MX+FX_s) on a support ;
whereby M is a metal of the 2"a, 3ra or 4th main group or any metal from a
sub-group of the periodic system of the elements, preferably aluminium ; B is
a
co-ordinately bound group ; x is in case of aluminium 3 ; y is any integer
between 1 and 3 ; b is 0 to 0.1 ; and x- b> y.
B is preferably an alkoxide, enolate or carboxylic acid group, more
preferably an alkoxide of the formula -O-C,Hzc+1 wherein c is any integer from
1
to 6 ; L is a solvent, preferably an anhydrous organic solvent selected from
the
group comprising alcohols, ethers, ketones, alkanes, aromatics ; and d is < 1.
In
one embodiment, d is 0.
The preparation of the supported precursor is preferably performed in a
waterfree solvent, preferably selected from the group consisting of alcohols,
ethers, ketones, alkanes, petroleum ether, formic acid, acetic acid or
propionic
acid. Alcohols of formula C,H2c+1OH with c = 1 to 6, especially 1 to 3, are
preferred.
The precursor can be obtained by reacting MX+BX, wherein B is preferably
an alkoxide, if the metal M is aluminium, B is more preferably propoxide,
dissolved or suspended in an organic solvent L, with anhydrous HF, preferably
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dissolved in an organic solvent L', whereby L' can be any of the solvents L
and
also L' can be equal to L. This is a so1-gel type reaction.
The method to apply a coating of the precursor on the support will now be
explained in detail for the preferred embodiment of amorphous aluminium
fluoride as supported catalyst.
The coating procedure can be performed in a manner principally known to
prepare catalytic coatings on catalyst supports. Two specific alternatives are
preferred. Both alternatives comprise a step a) or - as concerns the second
alternative - b) wherein a support coated with the precursor MX+F(X_s)_yByLd
or
MX+F(X_s)_yBy is formed, and a step c) wherein the activation takes place.
Alternative a) : According to the first preferred alternative, the support is
impregnated with the aluminium compound MX+BX ; M, B, x and y have the
meanings given above. After impregnation, the sol-gel reaction with HF,
preferably applied in a solvent, is performed to obtain the precursor.
In detail, the support, preferably thermally pretreated y-A1203, is given,
preferably under stirring, to a solution of a suitable organic aluminium
compound, preferably an aluminium alkoxide, more preferably aluminium
isopropoxide or methoxide, in an anhydrous organic solvent, preferably an
alcohol. If a doped supported catalyst is to be produced, a suitable organic
metal
compound of the respective metal or metals is added. Contact between support
and aluminium compound, preferably under stirring, is continued for a
sufficient
time to achieve the desired degree of impregnation. For example, after
addition
of the aluminium compound, the contact can be continued for equal to or more
than 10 minutes, preferably, for equal to or more than 20 minutes. The contact
can be extended, if desired, to a very long time, for example, more than 6
hours.
It is assumed that the longer the contact, the deeper the aluminium compound
or
precursor will penetrate into the support. Preferably, the contact between
support and aluminium compound is equal to or less than 6 hours, still more
preferably, equal to or less than 2 hours. Often, 20 minutes to 45 minutes are
very suitable.
Then, MX+BX, (here, M is preferably Al) is reacted with HF to transform it
into the precursor. A solution of anhydrous hydrogen fluoride in an organic
solvent, preferably in an Cl to C3 alcohol or in diethyl ether, is added,
preferably
under continued stirring, to the system of support and aluminium compound
MX+BX (M = Al). The amount of HF is selected so that the molar ratio of HF:Al
is preferably equal to or greater than 2. Preferably, it is equal to or lower
than 4.
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Very preferably, the molar ratio of HF:Al is 3 0,1. Most preferably, the
molar
ratio is 3. Preferably, the total amount of aluminium compound starting
material
(which is converted to the HS-A1F3 phase) in the system is adjusted to
correspond to an A1F3 content of the final catalyst of equal to or greater
than 3 %
by weight, more preferably equal to or more than 4 % by weight. Preferably,
the
content of aluminium fluoride in the supported catalyst is equal to or less
than
30 % by weight, more preferably equal to or less than 20 % by weight,
sometimes even equal to or less than 10 % by weight. Often, the amount is
adjusted so that the content of the HS-A1F3 phase in the supported catalyst is
between A highly preferred range is between 4 and 20 % by weight. Often, a
supported catalyst with 4 to 8 % by weight HS-A1F3 is produced.
Alternative b) According to the second preferred alternative, the organic
metal compound, preferably the aluminium compound, preferably in the form of
a solution, is first reacted in the so1-gel type reaction with the appropriate
amount
of HF solution, preferably under stirring, followed by addition of the
respective
support, whereby the materials used and their relative amounts are as
described
above, especially in view of the alternative a).
After the reaction of the aluminium compound and HF to form the
precursor has taken place, be it after impregnation of the carrier according
to the
first alternative, or before contact with the carrier according to the second
alternative, excessive solvent(s) is or are removed. Preferably, this is
performed
in a gentle manner, preferably under vacuum. The removal advantageously is
supported by warming or heating. Preferably, the temperature is equal to or
higher than 25 C, more preferably, it is equal to or higher than 30 C.
Preferably,
the temperature is equal to or lower than < 200 C, more preferably, it is
equal to
or lower than 150 C. A preferred range is 40 to 90 C. Both procedures a) or b)
and subsequent solvent removal provide a supported precursor, which, if y-
A1203
is used as support, can be described best by the formula of
MX+F(X_s)_yByLd/y-A1zO3, or, according to the other embodiment of EP 1440939,
is MX+F(X_s)_yBy /y-A12O3, with M, F, x, y, b, B, L and d as given above.
The precursor already has catalytic activity. The catalytic activity can be
greatly enhanced if the precursor is activated by subsequent fluorination with
a
gaseous fluorinating agent at elevated temperature, for example, with one or
more hydrochlorofluorocarbons or hydrofluorocarbons, especially with 1
or 2 carbon atoms, or with HF. The fluorinating agent is preferably admixed
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with an inert gas such as nitrogen or argon, whereby 10 up to 95 vol% inert
gas
can be used. In a preferred manner, the activation is performed applying
Al) CHC1F2 or CH2F2 or CHF3 or CH3F, or
A2) gaseous HF ; followed optionally by
B) flushing with inert gas, preferably nitrogen or a noble gas, for example,
argon,
providing a highly Lewis acidic supported HS-A1F3 catalyst, preferably on
y-A1203 of the formula A1F3_6/y-A12O3.
In step Al), CHC1F2 is the preferred fluorinating agent. It can be applied
in admixture with preferably mixed with up to 95 % (v/v), of an inert gas such
as
nitrogen or a noble gas, preferably argon ; the content of the inert gas is
preferably equal to or higher than 75 % (v/v) ; it is preferably equal to or
lower
than to 90 % (v/v). Especially preferably, the inert gas content is 83 2 %
(v/v).
The temperature in step Al) preferably is equal to or higher than 250 C, more
preferably, equal to or higher than 300 C. Preferably, the temperature is
equal to
or lower than 400 C. 340 C to 360 C is a very preferred range.
In the alternative step A2) wherein HF is used as fluorinating agent, the
temperature during treatment is preferably equal to or lower than 200 C ;
preferably, it is equal to or higher than 90 C. A temperature range from 75 C
to
150 C is very preferred, still more a range from 110 C to 130 C. HF preferably
is diluted with equal to or more than 80 % (v/v) of an inert gas, for example,
nitrogen or a noble gas, preferably argon. Preferably, the inert gas content
is
equal to or less than 97.5 % (v/v). An especially preferred content of inert
gas is
in the range of 95 2 % (v/v) of inert gas.
In step B), flushing is optionally performed to remove volatiles from the
catalyst. It is preferred to perform a flushing step. Flushing can be stopped
when the desired degree of purification has been achieved. It can be performed
for an extended time, for example, up to ten hours or more. Preferably,
flushing
is performed for equal to or less than 6 hours. Preferably, it is performed
for
equal to or more than 1 hour. The temperature during flushing is preferably
equal to or higher than 200 C. Preferably, it is equal to or lower than 300 C.
A
temperature range between 240 C and 260 C is very suitable. This is especially
advantageous if the activation was performed using HF.
Oxyfluorides on a support can be prepared as described in
WO 2006/058794. It includes a step of converting the precursor into an X-ray
amorphous oxide/hydroxyfluoride. This conversion can be performed by
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hydrolysis or thermal treatment of the precursor if it contains a metal-oxygen
bond.
It is to be noted that the manufacture of supported catalysts according to
the present invention as described herein is also applicable to other metal
fluorides and especially to mixtures of different metal fluorides resulting in
doped systems.
The supported catalyst can be prepared in the form of a powder, in the
form of pellets, beads, extrudates and other formed bodies. Beads with a
diameter in the range of, for example, 1 to 10 mmare very suitable for the
dehydrofluorination process.
The supported amorphous metal fluoride obtained has an extraordinary
high surface area, preferably in the range of 100 to 300 rri /g, as measured
according to the BET method using N2 (see [0091 ] of US 2006/052649 Al for
details) and in case of Lewis acidic metal ions an unusual high Lewis acidity,
which in case of aluminium fluoride, HS-A1F3, equals that of SbFs.
The supported metal catalyst, optionally doped, can be applied in many
fields. For example, it can be for halogen exchange reactions, especially for
the
chlorine-fluorine exchange of chlorohydrocarbons or chlorofluorohydrocarbons,
for example, with 1 to 5 carbon atoms. It also can be used for other reactions
where Lewis acid catalysts are applicable. It can be used for isomerisation
reactions of haloperfluoroalkanes, for the isomerisation of olefins, e.g. for
the
isomerisation of alkenes-l to alkenes-2, for the catalysis of Friedel-Crafts
acylation reactions as well as Friedel-Crafts alkylation reactions of aromatic
ring
systems. Especially preferably, the supported catalyst is applied in the
dehydrohalogenation process of the present invention.
Another aspect of the present invention are mixtures comprising or
consisting of nitrogen and a hydrofluorocarbon with 2 to 5 carbon atoms in a
molar ratio of N2:hydrofluorocarbon of (2 - 9):1, preferably of (3 - 6):1.
Mixtures comprising or consisting of nitrogen and a hydrofluorocarbon with 2
to
5 carbon atoms in a molar ratio of N2:hydrofluorocarbon of (3 - 5):l are
especially preferred. Especially preferred are mixtures comprising or
consisting
of N2 and a C3 or C4 hydrofluorocarbon in a molar ratio of (2 - 9):1,
preferably
(3 - 6):1, more preferably (3-5):1. Most preferred are mixtures consisting of
N2
and pentafluoropropane, hexafluoropropane, pentafluorobutane or
hexafluorobutane. In this embodiment, the hydrofluorocarbon is especially
preferably 1,1,1,2,3,3-hexafluoropropane, 1,1,1,3,3,3-hexafluoropropane,
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1,1,1,2,3,3-hexafluoropropane or, most preferred, 1, 1, 1,3,3 -
pentafluorobutane.
Mixtures consisting of nitrogen and 1, 1, 1,3,3-pentafluorobutane in a molar
ratio
ofNz:l,l,1,3,3-pentafluorobutane of (2 - 9):1, preferably (3 - 6):1, most
preferably 3 - 5):1 are especially preferred.
In the foregoing embodiment, the term "comprising" preferably denotes
compositions comprising the mixtures in an amount of at least 70 % by weight.
The remainder to 100 % by weight can, for example, be recycled reaction
mixture, optionally after separating off certain components. For example, if
it is
intended to produce 1,1,3-trifluorobutadiene, one can remove selectively the
1,1,3-trifluorobutadiene and can recycle unreacted 1,1,1,3,3-pentafluorobutane
starting material and the tetrafluorobutenes.
These gas (or vapour) mixtures are especially suitable for catalytic gas
phase dehydrofluorination reactions, especially when an aluminium fluoride
catalyst is used because it was observed that catalytic centres of the
catalyst
remain active in the presence of the reaction product hydrogen fluoride.
Without
intention to be limited by this explanation, it is assumed that the nitrogen
removes HF molecules adhering to the catalyst surface, thus reducing the
catalytic activity.
Another aspect of the present invention is to use nitrogen or inert gas in
admixture with a hydrofluoroalkane compound to remove HF from the surface of
dehydrofluorination catalysts in gas phase reactions, especially for aluminium
fluoride catalysts. Of course, it may occur that other compounds adhering to
the
catalyst surface are also removed. The gas (or vapour) mixtures can be
produced
before their introduction into a reactor, e.g. they can be prepared by mixing
the
components in a storage tank under pressure, or they can be produced in situ
in
the reactor.
The invention will be explained further by the following examples 1 to 9
without intending to limit it.
General Procedure for catalytic dehydrofluorination of HFCs
A stainless steel or fused silica tube reactor (8 mm ID, 380 mm length) was
loaded with powdery HS-A1F3 (catalyst A), prepared as described in EP
1440939. The bed of catalyst was held in the middle of the vertical reactor by
a
plug of silver or quartz wool. Dehydrofluorination experiments were performed
passing the respective N2 diluted HFC gas (HFC:N2 = 1:4 ; total flow
2.5 mL/min) at the indicated temperature through the reactor, the gaseous
effluents were passed through sodium fluoride pellets or aqueous potassium
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hydroxide solution to scrub HF and then analysed online by GC
(Shimadzu GC 17A with Porapak Q capillary column). In separate experiments
the products identified by GC were confirmed by 'H- and19F-NMR of there
solutions in CDC13.
Examplel : Dehydrofluorination of 1, 1, 1,2-tetrafluoroethane over catalyst A
Following the General Procedure the dehydro fluorination of
1,1,1,2-tetrafluoroethane, CF3-CFH2 (R 134a), was performed using 0.8 g
catalyst. The formation of trifluoroethylene as result of the
dehydrofluorination
over the catalyst was investigated at different temperatures, followed by on-
line
GC and confirmed by 'H and19F NMR spectroscopy.
Temperature, C : 200 250 300
Conversion, %
CF3-CFH2 1.0 6.2 10.8
Selectivity, %
CF2=CFH 30.6 71.2 89.0
Example 1.1 : Dehydrofluorination of 1,1,1,2-tetrafluoroethane over catalyst
A in a micro plant scale
Example 1 was repeated. This time, 20.25 g of the catalyst were placed in
a tube with 1 inch ID (inner diameter). The HFC-134a was supplied to the tube
with a flow 10.5 to 13 1/h, N2 was supplied with 7.1 1/h.
Content of HFC-1123 in the raw gas leaving the reactor :
Example No. Reaction temperature Content HFC-1123 in the raw gas
1.1.1 300 C 1.26 mass %
1.1.2 350 C 1.85 mass %
1.1.3 400 C 13.15 mass %
1.1.4 450 C 33.15 mass %
1.1.5 500 C 30.2lmass %
The productivity fell in the course of several hours, especially at higher
temperatures.
Example 2 : Dehydrofluorination of 1,1,1,2,3,3-hexafluoropropane
Following the General Procedure, the dehydrofluorination of
1,1,1,2,3,3-hexafluoropropane, CF3-CFH-CHF2 (HFC 236ea), was performed
using 0.7 g of catalyst. The results of the dehydrofluorination over the
catalyst at
different temperatures were followed by on-line GC and confirmed by 'H and 19F
NMR Spectroscopy.
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Temperature, C : 250 300 350
Conversion, % :
CF3-CFH-CHF2 7 19 95
Selectivity, %
CHF=CF- CF3 (Z) 100 89 88
CHF=CF- CF3 (E) 0 11 12
Example 3 : Dehydrofluorination of 1, 1, 1,3,3,3-hexafluoropropane
Following the General Procedure, the dehydrofluorination of
1, 1, 1,3,3,3-hexafluoropropane, CF3-CH2-CF3 (R 236fa) was performed using
0.62 g catalyst. The results of the dehydrofluorination over the catalyst at
different temperatures were followed by on-line GC and confirmed by 'H
and19F NMR Spectroscopy.
Temperature, C : 300 350 400
Conversion, %
CF3-CF2-CFH2 3 13.5 33.5
Selectivity, %
CF3-CH=CF2 9 88 66
Examples using a supported catalyst :
Example 4 : Manufacture of y-A120 supported HS-A1F3 precursor
Firstly, y-A1203 (10 g, pellets 3 mm diameter), calcined at 900 C in air for
12 hours whereby according to X-ray diffraction analysis no conversion to
a-A12O3 was detectable, was added to a stirred solution of aluminium
triisopropoxide (Al(O'Pr)3) (1.2 g) in water free isopropanol (15 mL).
Stirring
continued for about 0.5 hours, then 18 mMol hydrogen fluoride dissolved in
water free isopropanol (6 mL) were added and for about another 1.5 hours
stirred. The mixture was then placed in a rotary evaporator and at 70 C under
vacuum the solvent removed yielding about 11 g y-A120 supported HS-A1F3
precursor.
Example 5 : Manufacture of y-A120 supported HS-A1F3 (HS-A1F3/y-A1203)
Supported precursor prepared according to example 4 (about 2 g) was
loaded into a vertical stainless steel tube reactor on a silver wool plug. A
mixture of CHC1F2 (4 mL/min) and N2 (20 mL/min) was passed through the
sample and the temperature of the reactor was slowly increased up to 250 C.
After altogether 6 hours the reactor was cooled down and about 1.9 g catalyst,
corresponding to 4.9 % HS-A1F3 loading on the A1203, was taken out under
exclusion of moisture.
Example 6 : Catalytic activity of a catalyst comprising y-A120 supported
HS-A1F3 (HS-A1F3/y-A1203)
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As test reaction the catalytic isomerisation of
1,2-dibromohexafluoropropane to 2,2-dibromohexafluoropropane was studied,
which has to be catalysed by the strongest known Lewis acids (SbF5, ACF,
HS-A1F3). About 20 mg of HS-A1F3/y-A1203 was placed under exclusion of
moisture in a small glass vessel equipped with a magnetic stirrer bar and
sealed
with a rubber cap. Through the rubber cap, about 300 L CBrF2CBrFCF3 were
added with a syringe, and the mixture was stirred at room temperature for
2 hours. Then was a small amount of the liquid removed from the vessel, mixed
with CDC13 and subjected to 19F-NMR analysis. The analysis showed that 30 %
of CBrF2CBrFCF3 was converted to CF3CBr2CF3.
General Procedure for catalytic dehydrofluorination of HFCs
A stainless steel or fused silica tube reactor (8 mm ID, 380 mm length) was
loaded with HS-A1F3 supported by y-A1203 which was prepared as described in
example 2 above. The bed of catalyst was held in the middle of the vertical
reactor by a plug of silver or quartz wool. Dehydrofluorination experiments
were performed passing the respective N2 diluted HFC gas (HFC:N2 = 1:4 ; total
flow 2.5 mL/min) at the indicated temperature through the reactor, the gaseous
effluents were passed through sodium fluoride pellets or aqueous potassium
hydroxide solution to scrub HF and then analysed online by GC
(Shimadzu GC 17A with Porapak Q capillary column). In separate experiments
the products identified by GC were confirmed by 'H- and19F-NMR of there
solutions in CDC13.
Example 7: Dehydrofluorination of 1,1,1,2-tetrafluoroethane over the supported
catalyst
Following the General Procedure the dehydrofluorination of
1,1,1,2-tetrafluoroethane, CF3-CFH2 (R 134a), was performed using 2g of the
supported catalyst. The results of the dehydrofluorination over the catalyst
at
different temperatures were followed by on-line GC and confirmed by 'H
and19F NMR Spectroscopy.
Temperature, C : 200 250 300
Conversion, %
CF3-CFH2 1.1 5.8 12.2
Selectivity, %
CF2=CFH 24.6 68.9 83.7
Example 8 : Dehydrofluorination of 1,1,1,2,3,3-Hexafluoropropane over the
supported catalyst
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Following the General Procedure, the dehydrofluorination of
1,1,1,2,3,3-hexafluoropropane, CF3-CFH-CHF2 (R 236ea), was performed using
1.97 g of the supported catalyst. The results of the dehydrofluorination over
the
catalyst at different temperatures were followed by on-line GC and confirmed
by
'H and19F NMR Spectroscopy
Temperature, C : 250 300 350
Conversion, % :
CF3-CFH-CHF2 7 19 95
Selectivity, %
CHF=CF- CF3 (Z) 100 89 88
CHF=CF- CF3 (E) 0 11 12
Example 9 : Dehydrofluorination of 1,1,1,3,3-pentafluorobutane
A catalyst was used which was prepared as described above in example 4.
It contained 15 % by weight of HS-A1F3, supported on A1203 beads with a
diameter of about 3 mm.
A tube with 8 mm internal diameter, containing 0.76 g of the catalyst, was
used as reactor ; height of the catalyst in the tube : 4 cm. A mixture of
HFC-365mfc and nitrogen, molar ratio N2:HFC-365mfc kept at about 5, was
passed through the reactor at a given temperature.
The results measured by GC-MS are compiled in the following table. The
content of the different compounds is given in area-% of the GC :
Temperature C4F5H5 C4F4H41) C4F4H42) C4F4H43) C4F3H34)
307 C 7.7 27.8 40.9 20.8 1.5
347 C 6.9 24.5 36.5 19.4 8.6
1) Allocated to (E) 1,1,1,3 -tetrafluoro-but-2-ene, shortest retention time in
the
GC
2) Allocated to 2,4,4,4-tetrafluoro-l-butene
3) Allocated to (Z) 1,1,1,3-tetrafluoro-but-2-ene, longest retention time in
the
GC
4) 1, 1, 3 -trifluorobutadiene
The reaction was performed for several hours at 257 C and then several
hours at 350 C. The composition of the raw gas was essentially constant for
the
respective reaction temperature.
NMR data for 2,4,4,4-tetrafluorobutene :
13C:CF36=125,1ppm(q);CH26=35,3ppm;CF6=150,1ppm;
CH2=CF 6 = 35,3 ppm
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H : CH2 6= 3,17 ppm (dq) ; CH (cis to F on C2 atom) 6= 5,04 ppm(dd) ;
CH (trans to F on C2 atom) 6= 4,54 ppm(dd)
Example 4 was repeated in the micro pilot plant with respective higher
productivity using 19.9 g catalyst A. The volumetric gas flow was between 31
and 371/h. The results were comparable in view of the composition of the raw
gas. The data determined by GC-MS at several different temperatures are
compiled in the following table :
Temperature C4F5H5 C4F4H41) C4F4H42) C4F4H43) C4F3H34)
207 C 52.2 14.4 23 8.9 0.0
257 C 20.7 26.3 36.6 15.6 0.3
325 C 15.7 26.7 38.1 17.5 1.6
350 C 12.7 23.2 33.5 17.3 10.5
405 C 7.8 9.4 50.3 9.5 15.4
1) Allocated to (E) 1,1,1,3-tetrafluoro-but-2-ene, shortest retention time in
the GC
2) Allocated to 2,4,4,4-tetrafluoro-l-butene by IH and 13C NMR
3) Allocated to (Z) 1,1,1,3-tetrafluoro-but-2-ene, longest retention time in
the GC
4) 1, 1, 3 -trifluorobutadiene.
