Note: Descriptions are shown in the official language in which they were submitted.
CA 02854047 2014-04-30
PROCESS FOR PREPARING FORMIC ACID BY REACTION OF CARBON DIOXIDE
WITH HYDROGEN
Description
The invention relates to a process for preparing formic acid by reaction of
carbon dioxide
with hydrogen in a hydrogenation reactor in the presence of a transition metal
complex as
a catalyst comprising at least one element from group 8, 9 or 10 of the
Periodic Table and
at least one phosphine ligand with at least one organic radical having at
least 13 carbon
atoms, of a tertiary amine and of a polar solvent to form a formic acid-amine
adduct, which
is subsequently dissociated thermally to formic acid and the corresponding
tertiary amine.
Adducts of formic acid and tertiary amines can be dissociated thermally to
free formic acid
and tertiary amine, and therefore serve as intermediates in the preparation of
formic acid.
Formic acid is an important and versatile product. It is used, for example,
for acidification
in the production of animal feeds, as a preservative, as a disinfectant, as an
auxiliary in the
textile and leather industry, as a mixture with salts thereof for deicing of
vehicles and
runways for takeoff and landing, and as a synthesis unit in the chemical
industry.
Said adducts of formic acid and tertiary amines can be prepared in various
ways, for
example (i) by direct reaction of the tertiary amine with formic acid, (ii) by
hydrolysis of
methyl formate to formic acid in the presence of the tertiary amine, (iii) by
catalytic
hydration of carbon monoxide in the presence of the tertiary amine or (iv) by
hydrogenation of carbon dioxide to formic acid in the presence of the tertiary
amine. The
latter process for catalytic hydrogenation of carbon dioxide has the
particular advantage
that carbon dioxide is available in large volumes and is flexible with regard
to its source.
WO 2010/149507 describes a process for preparing formic acid by hydrogenation
of
carbon dioxide in the presence of a tertiary amine, of a transition metal
catalyst and of a
high-boiling polar solvent having an electrostatic factor
200*10-3 Cm, for example
ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol,
1,3-propanediol,
2-methyl-1,3-propanediol, 1,4-butanediol, dipropylene glycol, 1,5-pentanediol,
1,6-
hexanediol and glycerol. A reaction mixture is obtained which comprises the
formic acid-
amine adduct, the tertiary amine, the high-boiling polar solvent and the
catalyst. The
reaction mixture is worked up according to WO 2010/149507 by the following
steps:
1) phase separation of the reaction mixture to obtain an upper phase
comprising
the tertiary amine and the catalyst, and a lower phase comprising the formic
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acid-amine adduct, the high-boiling polar solvent and residues of the
catalyst;
recycling of the upper phase to the hydrogenation,
2) extraction of the lower phase with the tertiary amine to obtain an extract
comprising the tertiary amine and the residues of the catalyst, and a
raffinate
comprising the high-boiling polar solvent and the formic acid-amine adduct;
recycling of the extract to the hydrogenation,
3) thermal dissociation of the raffinate in a distillation column to obtain a
distillate
comprising the formic acid and a bottoms mixture comprising the free tertiary
amine and the high-boiling polar solvent; recycling of the high-boiling polar
solvent to the hydrogenation.
A disadvantage of the process of WO 2010/149507 is that the removal of the
catalyst is
incomplete in spite of phase separation (step 1)) and extraction (step 2)),
and so catalyst
traces present in the raffinate, in the course of thermal dissociation in the
distillation
column in step 3), can catalyze the redissociation of the formic acid-amine
adduct to
carbon dioxide and hydrogen and the tertiary amine according to the following
equation:
Cat
H CO OH *N R3 --10' C 02 + H2+ N R3
The redissociation leads to a distinct decrease in the yield of adduct of
formic acid and
tertiary amine, and hence to a decrease in the yield of the formic acid target
product.
A further disadvantage is that, in the course of thermal dissociation of the
formic acid-
amine adduct in the distillation column, there is esterification of the formic
acid formed with
the high-boiling polar solvents (diols and polyols). This leads to a further
reduction in the
yield of the formic acid target product.
It is an object of the present invention to provide a process for preparing
formic acid by
hydrogenation of carbon dioxide, with which substantially complete removal of
the catalyst
is enabled. The novel process shall have said disadvantages of the prior art
only to a
distinctly reduced degree, if at all, and lead to concentrated formic acid in
high yield and
high purity. In addition, the process shall allow a simpler process regime
than that
described in the prior art, more particularly a simpler process design for
workup of the
output from the hydrogenation reactor, simpler process stages, a smaller
number of
process stages or simpler apparatus. In addition, it shall also be possible to
perform the
process with a very low energy requirement.
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The object is achieved by a process for preparing formic acid, comprising the
steps of
(a) homogeneously catalyzed reaction of a reaction mixture (Rg) comprising
carbon dioxide, hydrogen, at least one polar solvent selected from the group
consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol,
2-methyl-1 -propanol and water, and a tertiary amine of the general formula
(Al)
NR1R2R3 (Al)
in which
R1, 1-=-.2,
R3 are each independently an unbranched or branched, acyclic or
cyclic, aliphatic, araliphatic or aromatic radical having in each case 1 to
16 carbon atoms, where individual carbon atoms may each
independently also be substituted by a hetero group selected from the -
0- and >N- groups, and two or all three radicals may also be joined to
one another to form a chain comprising at least four atoms in each case,
in the presence of at least one transition metal complex as a catalyst,
comprising at least one element selected from groups 8, 9 and 10 of the
Periodic Table and at least one phosphine ligand with at least one organic
radical having at least 13 carbon atoms,
in a hydrogenation reactor
to obtain, optionally after addition of water, a biphasic hydrogenation
mixture
(H) comprising
an upper phase (U1) comprising the catalyst and the tertiary amine (Al), and
a lower phase (L1) comprising the at least one polar solvent, residues of the
catalyst and a formic acid-amine adduct of the general formula (A2)
NR1R2R3* x, HCOOH (A2)
in which
x, is in the range from 0.4 to 5 and
R1, R2, R3 are each as defined above,
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(b) workup of the hydrogenation mixture (H) obtained in step (a) according to
one
of the following steps:
(bl) phase separation of the hydrogenation mixture (H) obtained in step (a)
in a first phase separation apparatus into the upper phase (U1) and
the lower phase (L1),
or
(b2) extraction of the catalyst from the hydrogenation mixture (H) obtained
in step (a) in an extraction unit with an extractant comprising a tertiary
amine (Al) to obtain
a raffinate (R1) comprising the formic acid-amine adduct (A2) and the
at least one polar solvent and
an extract (El) comprising the tertiary amine (Al) and the catalyst
or
(b3) phase separation of the hydrogenation mixture (H) obtained in step (a)
in a first phase separation apparatus into the upper phase (U1) and
the lower phase (L1) and extraction of the residues of the catalyst
from the lower phase (L1) in an extraction unit with an extractant
comprising a tertiary amine (Al) to obtain
a raffinate (R2) comprising the formic acid-amine adduct (A2) and the
at least one polar solvent and
an extract (E2) comprising the tertiary amine (Al) and the residues of
the catalyst,
(c) separation of the at least one polar solvent from the lower phase (L1),
from the
raffinate (R1) or from the raffinate (R2) in a first distillation apparatus to
obtain
a distillate (DI) comprising the at least one polar solvent, which is recycled
into
the hydrogenation reactor in step (a), and
a biphasic bottoms mixture (B1) comprising
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an upper phase (U2) comprising the tertiary amine (Al), and a lower phase
(L2) comprising the formic acid-amine adduct (A2),
(d) optional workup of the bottoms mixture (B1) obtained in step (c) by phase
5
separation in a second phase separation apparatus into the upper phase (U2)
and the lower phase (L2),
(e) dissociation of the formic acid-amine adduct (A2) present in the bottoms
mixture (B1) and/or possibly in the lower phase (L2) in a thermal dissociation
unit to obtain the corresponding tertiary amine (Al), which is recycled to the
hydrogenation reactor in step (a), and formic acid, which is discharged from
the thermal dissociation unit.
It has been found that formic acid is obtainable in high yield by the process
according to
the invention. The process according to the invention enables more effective
removal of
the transition metal complex used as the catalyst compared to the prior art,
and the
recycling thereof into the hydrogenation reactor in step (a). This very
substantially prevents
the redissociation of the formic acid-amine adduct (A2), which leads to an
increase in the
formic acid yield. The removal of the polar solvent used in accordance with
the invention
additionally prevents esterification of the formic acid obtained in the
thermal dissociation
unit in step (e), which likewise leads to a rise in the formic acid yield. In
addition, it has
been found that, surprisingly, the use of the inventive polar solvent leads to
an increase in
the concentration of the formic acid-amine adduct (A2) in the hydrogenation
mixture (H)
obtained in step (a) - compared to the high-boiling polar solvents used in
W02010/149507.
This enables the use of smaller reactors, which in turn leads to a cost
saving.
The terms "step" and "process stage" are used synonymously hereinafter.
Preparation of the formic acid-amine adduct (A2): process stage (a)
In the process according to the invention, in process stage (a), in a
hydrogenation reactor,
there is conversion of a reaction mixture (Rg) comprising carbon dioxide,
hydrogen, at
least one polar solvent selected from the group consisting of methanol,
ethanol, 1-
propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol and water, and a tertiary
amine of the
general formula (Al). The reaction is effected in the presence of a catalyst.
The catalyst
used is at least one transition metal complex comprising at least one element
selected
from groups 8, 9 and 10 of the Periodic Table and at least one phosphine
ligand having at
least 13 carbon atoms.
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The carbon dioxide used in process stage (a) may be solid, liquid or gaseous.
It is also
possible to use gas mixtures which comprise carbon dioxide and are available
on the
industrial scale, provided that they are substantially free of carbon monoxide
(proportion by
volume of < 1% CO). The hydrogen used in the hydrogenation of carbon dioxide
in
process stage (a) is generally gaseous. Carbon dioxide and hydrogen may also
comprise
inert gases, for instance nitrogen or noble gases. Advantageously, however,
the content
thereof is below 10 mol%, based on the total amount of carbon dioxide and
hydrogen in
the hydrogenation reactor. Larger amounts may likewise still be tolerable in
some cases,
but generally cause the employment of a higher pressure in the reactor, the
result of which
is that further compression energy is required.
Carbon dioxide and hydrogen can be fed to process stage (a) as separate
streams. It is
also possible to use a mixture comprising carbon dioxide and hydrogen in
process stage
(a).
In the process according to the invention, in process stage (a), at least one
tertiary amine
(Al) is used in the hydrogenation of carbon dioxide. In the context of the
present invention,
"tertiary amine (Al)" is understood to mean either one (1) tertiary amine (Al)
or mixtures
of two or more tertiary amines (Al).
The tertiary amine (Al) used in the process according to the invention is
preferably
selected such that or matched to the polar solvent such that the hydrogenation
mixture (H)
obtained in process stage (a), optionally after addition of water, is at least
biphasic. The
hydrogenation mixture (H) comprises an upper phase (U1), which comprises the
catalyst
and the tertiary amine (Al), and a lower phase (L1), which comprises the at
least one
polar solvent, residues of the catalyst and a formic acid-amine adduct (A2).
The tertiary amine (Al) is present enriched in the upper phase (U1), which
means that the
upper phase (U1) comprises the majority of the tertiary amine (Al). "Enriched"
or
"majority" with regard to the tertiary amine (Al) should be understood in the
context of the
present invention to mean a proportion by weight of the free tertiary amine
(Al) in the
upper phase (U1) of > 50% based on the total weight of the free tertiary amine
(Al) in the
liquid phases, i.e. the upper phase (U1) and the lower phase (L1) in the
hydrogenation
mixture (H).
Free tertiary amine (Al) is understood to mean the tertiary amine (Al) not
bound in the
form of the formic acid-amine adduct (A2).
Preferably, the proportion by weight of the free tertiary amine (Al) in the
upper phase (U1)
is > 70%, especially > 90%, based in each case on the total weight of the free
tertiary
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amine (Al) in the upper phase (U1) and the lower phase (L1) in the
hydrogenation mixture
(H).
The tertiary amine (Al) is generally selected by a simple test in which the
phase behavior
and the solubility of the tertiary amine (Al) in the liquid phases (upper
phase (U1) and
lower phase (L1)) is determined experimentally under the process conditions in
process
stage (a). It is additionally possible to add nonpolar solvents to the
tertiary amine (Al), for
example aliphatic, aromatic or araliphatic solvents. Preferred nonpolar
solvents are, for
example, octane, toluene and/or xylenes (o-xylene, m-xylene, p-xylene).
Preference is given to tertiary amine of the general formula (Al) in which the
R1, R2, R3
radicals are the same or different and each independently an unbranched or
branched,
acyclic or cyclic, aliphatic, araliphatic or aromatic radical having in each
case 1 to 16
carbon atoms, preferably 1 to 12 carbon atoms, where individual carbon atoms
may each
independently also be substituted by a hetero group selected from the -0- and
>N- groups,
and two or all three radicals may also be joined to one another to form a
chain comprising
at least four atoms in each case. In a particularly preferred embodiment, a
tertiary amine of
the general formula (Al) is used, with the proviso that the total number of
carbon atoms is
at least 9. =
Examples of suitable tertiary amines (Al) include:
= tri-n-propylamine, tri-n-butylamine, tri-n-pentylamine, tri-n-hexylamine,
tri-n-
heptylamine, tri-n-octylamine, tri-n-nonylamine, tri-n-decylamine, tri-n-
undecylamine,
tri-n-dodecylamine, tri-n-tridecylamine, tri-n-tetradecylamine, tri-n-
pentadecylamine,
tri-n-hexadecylamine, tri(2-ethylhexyl)amine.
= dimethyldecylamine, dimethyldodecylamine, dimethyltetradecylamine,
ethyldi(2-
propyl)amine, dioctylmethylamine, dihexylmethylamine.
= tricyclopentylamine, tricyclohexylamine, tricycloheptylamine,
tricyclooctylamine, and
the derivatives thereof substituted by one or more methyl, ethyl, 1-propyl, 2-
propyl, 1-
butyl, 2-butyl or 2-methyl-2-propyl groups.
= dimethylcyclohexylamine, methyldicyclohexylamine, diethylcyclohexylamine,
ethyldicyclohexylamine, dimethylcyclopentylamine, methyldicyclopentylamine.
= triphenylamine, methyldiphenylamine, ethyldiphenylamine,
propyldiphenylamine,
butyldiphenylamine, 2-ethylhexyldiphenylamine,
dimethylphenylamine,
diethylphenylamine, dipropylphenylamine,
dibutylphenylamine, bis(2-
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ethylhexyl)phenylamine, tribenzylamine, methyldibenzylamine,
ethyldibenzylamine,
and the derivatives thereof substituted by one or more methyl, ethyl, 1-
propyl, 2-
propyl, 1-butyl, 2-butyl or 2-methyl-2-propyl groups.
= N-C1- to -C12-alkylpiperidines, N,N-di-C1- to -C12-alkylpiperazines, N-C1-
to -C12-
alkylpyrrolidones, N-C1- to -C12-alkylimidazoles, and the derivatives thereof
substituted
by one or more methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl or 2-methyl-
2-propyl
groups.
= 1,8-diazabicyclo[5.4.0]undec-7-ene ("DBU"), 1,4-diazabicyclo[2.2.2]octane
("DAB-
CO"), N-methyl-8-azabicyclo[3.2.1]octane ("tropane"),
N-methy1-9-
azabicyclo[3.3.1]nonane ("granatane"), 1-azabicyclo[2.2.2]octane
("quinuclidine").
In the process according to the invention, it is also possible to use mixtures
of two or more
different tertiary amines (Al).
Especially preferably, the tertiary amine (Al) used in the process according
to the
invention is an amine in which the R1, R2, R3 radicals are each independently
selected
from the group of C1- to C12-alkyl, C5- to Crcycloalkyl, benzyl and phenyl.
Especially preferably, the tertiary amine (Al) used in the process according
to the
invention is a saturated amine, i.e. an amine comprising only single bonds.
Very especially preferably, the tertiary amine used in the process according
to the
invention is an amine of the general formula (Al) in which the R1, R2, R3
radicals are each
independently selected from the group of C5- to CB-alkyl, especially tri-n-
pentylamine, tri-n-
hexylamine, tri-n-heptylamine, tri-n-octylamine,
dimethylcyclohexylamine,
methyldicyclohexylamine, dioctylmethylamine and dimethyldecylamine.
In one embodiment of the process according to the invention, one (1) tertiary
amine of the
general formula (Al) is used.
More particularly, the tertiary amine used is an amine of the general formula
(Al) in which
the R1, R2, R3 radicals are each independently selected from C5- and CB-alkyl.
Most
preferably, the tertiary amine of the general formula (Al) used in the process
according to
the invention is tri-n-hexylamine.
Preferably, the tertiary amine (Al) in all process stages of the process
according to the
invention is in liquid form. However, this is not an absolute requirement. It
would also be
sufficient if the tertiary amine (Al) were at least dissolved in suitable
solvents. Suitable
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solvents are in principle those which are chemically inert with respect to the
hydrogenation
of carbon dioxide, in which the tertiary amine (Al) and the catalyst are of
good solubility,
and in which, conversely, the polar solvent and the formic acid-amine adduct
(A2) are of
sparing solubility. Possible solvents therefore in principle include
chemically inert, nonpolar
solvents, for instance aliphatic, aromatic or araliphatic hydrocarbons, for
example octane
and higher alkanes, toluene, xylenes.
In the process according to the invention, in process stage (a), at least one
polar solvent
selected from the group consisting of methanol, ethanol, 1-propanol, 2-
propanol, 1-
butanol, 2-butanol, 2-methyl-l-propanol and water is used in the hydrogenation
of carbon
dioxide.
A "polar solvent" in the context of the present invention is understood to
mean either one
(1) polar solvent or mixtures of two or more polar solvents.
The polar solvent is preferably selected such that the hydrogenation mixture
(H) obtained
in process stage (a), optionally after addition of water, is at least
biphasic. The polar
solvent should be present enriched in the lower phase (L1), i.e. the lower
phase (L1)
should comprise the majority of the polar solvent. "Enriched" or "majority"
with regard to
the polar solvent should be understood in the context of the present invention
to mean a
proportion by weight of the polar solvent in the lower phase (L1) of > 50%
based on the
total weight of the polar solvent in the liquid phases (upper phase (U1) and
lower phase
(L1)) in the hydrogenation reactor.
Preferably, the proportion by weight of the polar solvent in the lower phase
(L1) is > 70%,
especially > 90%, based in each case on the total weight of the polar solvent
in the upper
phase (U1) and the lower phase (L1).
The polar solvent which fulfills the above criteria is generally selected by a
simple test in
which the phase behavior and the solubility of the polar solvent in the liquid
phases (upper
phase (U1) and lower phase (L1)) are determined experimentally under the
process
conditions in process stage (a).
The polar solvent may be a pure polar solvent or a mixture of two or more
polar solvents.
In one embodiment of the process according to the invention, in step (a), a
monophasic
hydrogenation mixture is first obtained, which is converted by the addition of
water to the
biphasic hydrogenation mixture (H).
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In a further embodiment of the process according to the invention, in step
(a), the biphasic
hydrogenation mixture (H) is obtained directly. The biphasic hydrogenation
mixture (H)
obtained by this embodiment can be supplied directly to the workup according
to step (b).
It is also possible to additionally add water to the biphasic hydrogenation
mixture (H)
5 before the further workup in step (b). This can lead to an increase in
the partition
coefficient PK=
In a further particularly preferred embodiment, the polar solvent used is
water, methanol or
a mixture of water and methanol.
The use of diols and the formic esters thereof, polyols and the formic esters
thereof,
sulfones, sulfoxides and open-chain or cyclic amides as the polar solvent is
not preferred.
In a preferred embodiment, these polar solvents are not present in the
reaction mixture
(Rg).
The molar ratio of the polar solvent or solvent mixture used in process stage
(a) in the
process according to the invention to the tertiary amine (Al) used is
generally 0.5 to 30
and preferably 1 to 20.
The transition metal complex used as the catalyst for hydrogenation of carbon
dioxide in
process stage (a) in the process according to the invention comprises at least
one element
selected from groups 8, 9 and 10 of the Periodic Table (IUPAC nomenclature)
and at least
one phosphine ligand with at least one organic radical having at least 13
carbon atoms.
Groups 8, 9 and 10 of the Periodic Table comprise Fe, Co, Ni, Ru, Rh, Pd, Os,
Ir and Pt. In
process stage (a), the catalyst used may be one (1) transition metal complex
or a mixture
of two or more transition metal complexes. "Transition metal complex" is
understood in the
context of the present invention to mean either one (1) transition metal
complex or mixture
of two or more transition metal complexes.
Preferably, the transition metal complex used as the catalyst comprises at
least one
element from the group consisting of Ru, Rh, Pd, Os, Ir and Pt, especially
preferably at
least one element from the group consisting of Ru, Rh and Pd. Very especially
preferably,
the transition metal complex comprises Ru.
Transition metal complexes preferred as catalysts comprise at least one
phosphine ligand
with at least one organic radical having 13 to 30 carbon atoms, preferably
having 14 to 26
carbon atoms, more preferably having 14 to 22 carbon atoms, especially
preferably having
15 to 22 carbon atoms, especially having 16 to 20 carbon atoms, where the
organic radical
is bonded to a phosphorus atom of the phosphine ligand.
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In a further preferred embodiment, the transition metal complexes used as
catalysts
comprise at least one bidentate phosphine ligand of the general formula (I)
R15 R16
(CHOn (CH2)m
I I
P P
R11/ \ / R14
R12 R13
(I)
in which .
R11, R12, R13, 1-K.-.14
are each independently unsubstituted or at least monosubstituted
-C13-C30-alkyl,
-(phenyl)-(C7-C24-alkyl),
-(phenyl)-(C4-C24-alky1)2, -(phenyl)-(C3-C24-alky1)3, -(phenyl)-(0-
C7-C24-alkyl), -(phenyl)-(0-C4-C24-alky1)2, -(phenyl)-(0-C3-C24-
alky1)3, -(cyclohexyl)-(C7-C24-alkyl), -(cyclohexyl)-(C4-C24-alkY1)2, -
(cyclohexyl)-(C3-C24-alky1)3, -
(cyclohexyl)-(0-C7-C24-alkyl), -
(cyclohexyl)-(0-C4-C24-alky1)2
or
-(cyclohexyl)-(0-C3-C24-alky1)3,
where the substituents are selected from the group consisting of
-F, -Cl, -Br, -OH, ¨0Ra, -COOH,
-COORa,
-000Ra, -CN, -NH2, -N(Ra)2 and -NHRa;
R", R16 are each independently hydrogen or -C1-C4-alkyl or, together
with
the carbon atoms to which they are bonded, form an
unsubstituted or at least monosubstituted phenyl or cyclohexyl
ring,
where the substituents are selected from the group consisting of
-000Ra, -000CF3, -0S02Ra, -0S02CF3,
-CN, -OH, -0Ra, -N(Ra)2, -NHRa and -C1-C4-alkyl;
Ra is -C1-C4-alkyl and
n, m are each independently 0, 1 or 2.
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¨C13-C30-Alkyl, in relation to the R11, R12, R13 and R14 radicals, is
understood in the context
of the present invention to mean linear or branched alkyl radicals having 13
to 30 carbon
atoms. These radicals comprise linear or branched alkyl radicals selected from
the group
consisting of tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl,
octadecyl, nonadecyl,
eicosyl, heneicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl,
heptacosyl,
octacosyl, nonacosyl and triacontyl. The -C13-C30-alkyl radicals are
preferably unbranched,
i.e. linear.
Preferred alkyl radicals (-C13-C30-alkyl) are linear or branched alkyl
radicals having 14 to 26
(¨C14-C26-alkyl), more preferably having 14 to 22 (¨C14-C22-alkyl), especially
preferably
having 15 to 22 (¨C15-C22-alkyl) and especially having 16 to 20 (¨C16-C20-
alkyl) carbon
atoms, preference being given to linear alkyl radicals.
12,
-
¨(Phenyl)-(C7-C24-alkyl), in relation to the R11, K
R13 and R14 radicals, is understood in
the context of the present invention to mean radicals of the general formula
(II) which are
bonded via the phenyl ring to the phosphorus atom of the phosphine ligand (I).
The -C7-
C24-alkyl radicals may be bonded to the phenyl ring in the 2, 3 or 4 position
and may be
linear or branched. The phenyl ring preferably does not bear any further
substituents apart
from the -C7-C24-alkyl radical. The -C7-C24-alkyl radicals may be
unsubstituted or at least
monosubstituted. The -C7-C24-alkyl radicals are preferably linear and
unsubstituted.
Preferred alkyl radicals in the ¨(phenyl)-(C7-C24-alkyl) radical are linear or
branched alkyl
radicals having 7 to 18 (i.e. ¨(phenyl)-(C7-C18-alkyl)). Particular preference
is given to alkyl
radicals having 7 to 12 carbon atoms (i.e. ¨(phenyl)-(C7-C12-alkyl)).
¨(Phenyl)-(0-C6-C24-alkyl), in relation to the R11, R12, R13 and K.-.14
radicals, is understood in
the context of the present invention to mean radicals of the general formula
(II) which are
bonded via the phenyl ring to the phosphorus atom of the phosphine ligand (I).
The -0-C7--
C24-alkyl radicals may be bonded to the phenyl ring via the oxygen in the 2, 3
or 4 position
and may be linear or branched. The phenyl ring preferably does not bear any
further
substituents apart from the -C7-C24-alkyl radical. The -0-C7-C24-alkyl
radicals may be
unsubstituted or at least monosubstituted. The -C7-C24-alkyl radicals are
preferably linear
and unsubstituted. Preferred alkyl radicals in the ¨(phenyl)-(O-C7-C24-alkyl)
radical are
linear or branched alkyl radicals having 7 to 18 carbon atoms (i.e. ¨(phenyl)-
(0-C7-C18-
alkyl)). Particular preference is given to alkyl radicals having 7 to 12
carbon atoms (i.e. ¨
(phenyl)-(0-C7-C12-alkyl)).
¨(Cyclohexyl)-(C7-C24-alkyl), in relation to the R11, r,12, R13 and R14
radicals, is understood
in the context of the present invention to mean radicals of the general
formula (IV) which
are bonded via the cyclohexyl ring to the phosphorus atom of the phosphine
ligand (I). The
-C7-C24-alkyl radicals may be bonded to the cyclohexyl ring in the 2, 3 or 4
position and
CA 02854047 2014-04-30
13
may be linear or branched. The cyclohexyl ring preferably does not bear any
further
substituents apart from the -C7-C24-alkyl radical. The -C7-C24-alkyl radicals
may be
unsubstituted or at least monosubstituted. The -C7-C24-alkyl radicals are
preferably linear
and unsubstituted. Preferred alkyl radicals in the ¨(cyclohexyl)-(C7-C24-
alkyl) radical are
linear or branched alkyl radicals having 7 to 18 carbon atoms (i.e.
¨(cyclohexyl)-(C7-C18-
alkyl)). Particular preference is given to alkyl radicals having 7 to 12
carbon atoms (i.e. ¨
(cyclohexyl)-(C7-C12-alkyl)).
¨(Cyclohexyl)-(0-C7-C24-alkyl), in relation to the R11, R12, 1-1 .-.13
and R14 radicals, is
/ ..),...(C7-C24-Alkyl)
urvvv,( / __ >0-(C7-C24-Alky1)
__________________________ 2 -
II III
ivl<
> (c7-AikYI)
ul
>0-(C7-C24-AikY0
__________________________ )
IV v
The wavy bond in the formulae II, Ill, IV and V indicates the bond of the
phenyl or
cyclohexyl ring to the phosphorus atom of the phosphine ligand (I) (1
position).
In the formulae II, III, IV and V, the -C7-C24-alkyl or the -0-C7-C24-alkyl
radicals are bonded
to the phenyl rings or the cyclohexyl rings preferably in the 4 position. The
phenyl rings or
cyclohexyl rings preferably bear, in the 4 position, a ¨C7-C18-alkyl or -0-C7-
C18-alkyl
radical. The phenyl rings or cyclohexyl rings especially preferably bear, in
the 4 position, a
¨C7-C12-alkyl or -0-C7-C12-alkyl radical.
CA 02854047 2014-04-30
14
¨(Phenyl)-(C4-C24-alky1)2, in relation to the R", 1312, R13 and R14 radicals,
is understood in
the context of the present invention to mean radicals which are bonded via the
phenyl ring
to the phosphorus atom of the phosphine ligand (I) and the phenyl ring bears
two ¨C4-C24-
alkyl radicals. The ¨C4-C24-alkyl radicals may be bonded to the phenyl ring in
the (2,3),
(2,4), (2,5), (2,6), (3,4) or (3,5) positions, preference being given to the
(3,5) position. The
¨C4-C24-alkyl radicals may be linear or branched. The phenyl ring preferably
does not bear
any further substituents apart from the two -C4-C24-alkyl radicals. The -C4-
C24-alkyl radicals
may be unsubstituted or at least monosubstituted. The -C4-C24-alkyl radicals
are preferably
unsubstituted.
Preferred alkyl radicals in the ¨(phenyl)-(C4-C24-alky1)2 radical are linear
or branched alkyl
radicals having 4 to 18 (i.e. ¨(phenyl)-(C4-C18-alkyl))2. Particular
preference is given to alkyl
radicals having 4 to 12 carbon atoms (i.e. ¨(phenyl)-(C4-C12-alkyl))2 and
especially having
4 to 6 carbon atoms (i.e. ¨(phenyl)-(C4-C6-alkyl))2. An example of a suitable
alkyl radical is
tert-butyl.
12,
-
¨(Phenyl)-(0-C4-C24-alky1)2, in relation to the R11, KR13 and R14 radicals, is
understood
in the context of the present invention to mean radicals which are bonded via
the phenyl
ring to the phosphorus atom of the phosphine ligand (I) and the phenyl ring
bears two ¨0-
C4-C24-alkyl radicals. The ¨0-C4-C24-alkyl radicals may be bonded to the
phenyl ring in the
(2,3), (2,4), (2,5), (2,6), (3,4) or (3,5) positions, preference being given
to the (3,5) position.
The ¨0-C4-C24-alkyl radicals may be linear or branched. The phenyl ring
preferably does
not bear any further substituents apart from the two -0-C4-C24-alkyl radicals.
The -0-C4-
C24-alkyl radicals may be unsubstituted or at least monosubstituted. The -0-C4-
C24-alkyl
radicals are preferably unsubstituted.
Preferred alkyl radicals in the ¨(phenyl)-(0-C4-C24-alky1)2 radical are linear
or branched
alkyl radicals having 4 to 18 (i.e. ¨(phenyl)-(0-C4-C18-alkyl))2. Particular
preference is given
to alkyl radicals having 4 to 12 carbon atoms (i.e. ¨(phenyl)-(0-C4-C12-
alkyl))2 and
especially having 4 to 6 carbon atoms (i.e. ¨(phenyl)-(0-C4-C6-alkyl))2. An
example of a
suitable -0-alkyl radical is tert-butoxy.
For ¨(cyclohexyl)-(C4-C24-alky1)2 and ¨(cyclohexyl)-(0-C4-C24-alky1)2, the
above details and
preferences for ¨(phenyl)-(C4-C24-alky1)2 and -(phenyl)-(0-C4-C24-alky1)2
apply
correspondingly.
-(Phenyl)-(C3-C24-alky03, -(phenyl)-(0-C3-C24-alky1)3, -(cyclohexyl)-(C3-
C24-alkyl)3, -
(cyclohexyl)-(0-C3-C24-alkyl) and -(cyclohexyl)-(0-C3-C24-alky1)3 are
understood to mean
phenyl and cyclohexyl rings which are bonded to the phosphorus atom of the
phosphine
ligand (I) in the 1 position, the phenyl or cyclohexyl ring bearing three ¨C3-
C24-alkyl
radicals or three ¨0-C3-C24-alkyl radicals. The -C3-C24-alkyl or -0-C3-C24-
alkyl radicals may
CA 02854047 2014-04-30
be bonded to the phenyl or cyclohexyl ring in the (2,3,4), (2,3,5), (2,4,6),
(3,4,5) or (2,3,6)
positions.
Particular preference is given to phosphine ligands (I) in which the R11, R12,
R13 and R14
5 radicals are the same.
Particular preference is further given to phosphine ligands of the general
formula (I) in
which
10
R11, R12, IV, R14 are each independently unsubstituted or at least
monosubstituted -C13-
C30-alkyl,
-(phenyl)-(C7-C24-alkyl),
-(Phenyl)-(C4-C24-alky1)2, -(phenyl)-(0-C7-C24-alkyl), -(phenyl)-(0-C4-C24-
alky1)2, -(cyclohexyl)-(C7-C24-alkyl), -(cyclohexyl)-(C4-C24-alky1)2, -
(cyclohexyl)-(0-C7-C24-alkyl) or -(cyclohexyl)-(0-C4-C24-alky1)2,
15 where the substituents are selected from the group consisting
of -F, -Cl,
-Br, -OH, -0Ra, -COOH,
-COORa,
-000Ra, -CN, -N H2, -N(Ra)2 and -NHFRa;
R15, R16 are each independently hydrogen or -C1-C4-alkyl or,
together with the
carbon atoms to which they are bonded, form an unsubstituted or at
least monosubstituted phenyl or cyclohexyl ring,
where the substituents are selected from the group consisting of -
OCORa, -0000F3, -0S02Ra,
-0S02CF3,
-CN, -OH, -0Ra, -N(Ra)2, -NHRa and -C1-C4-alkyl;
Ra is -C1-C4-alkyl and
n, m are both 0, 1 or 2, preferably both 0 or 1, especially
both 0.
Particular preference is further given to phosphine ligands of the general
formula (I) in
which
R11, R12, R13, 1-(=-=.14
are each independently unsubstituted or at least monosubstituted -C13-
C30-alkyl,
-(phenyl)-(C7-C24-alkyl),
-(phenyl)-(0-C7-C24-alkyl), -(cyclohexyl)-(C7-C24-alkyl) or
-(cyclohexyl)-(0-C7-C24-alkyl),
where the substituents are selected from the group consisting of -F, -Cl,
-Br, -OH, -0Ra, -COOH,
-COORa,
-000Ra, -CN, -NH2, -N(Ra)2 and -NHRa;
CA 02854047 2014-04-30
16
R15, R16 are each independently hydrogen or -C1-C4-alkyl or,
together with the
carbon atoms to which they are bonded, form an unsubstituted or at
least monosubstituted phenyl or cyclohexyl ring,
where the substituents are selected from the group consisting of -
OCORa, -0000F3, -0S02Ra, = -0S02CF3,
-CN, -OH, -OR', -N(Ra)2, -NHRa and -C1-C4-alkyl;
Ra is -C1-C4-alkyl and
n, m are both 0, 1 or 2, preferably both 0 or 1, especially both 0.
Particular preference is further given to phosphine ligands of the general
formula (I) in
which
R11, R12, R13, K=-=14
are each independently unsubstituted or at least monosubstituted
-C i3-C38-alkyl,
where the substituents are selected from the group consisting of
-F, -Cl, -Br, -OH, ¨OR', -COOH,
-COORa,
-000Ra, -CN, -N H2, -N(Ra)2 and -NHRa;
R15, R16 are each independently hydrogen or -C1-C4-alkyl,
is -C1-C4-alkyl and
n, m are both 0.
More preferred are phosphine ligands of the general formula (I) in which
R11, R12, R13, K.-.14
are each independently unsubstituted -C13-C30-alkyl;
R15, R16 are both hydrogen and
n, m are both 0.
Most preferred are phosphine ligands of the general formula (I) in which
R11, R12, R13, K.-.14
are all unsubstituted -C12-C20-alkyl, preferably unsubstituted C12-
C18-alkyl and more preferably C13-C18-alkyl;
CA 02854047 2014-04-30
17
R15, R16 are both hydrogen and
n, m are both 0.
Particularly preferred bidentate phosphine ligands (I) are selected from the
group
consisting of 1,2-bis(ditetradecylphosphino)ethane, 1 ,2-
bis(dipentadecylphosphino)ethane,
1 ,2-bis(dihexadecylphosphino)ethane and 1,2-bis(dioctadecylphosphino)ethane.
Phosphine ligands of the general formula (I) in which n and m are both 0 are
obtainable,
for example, by reaction of 1 ,2-bis(dichlorophosphino)ethane compounds of the
general
formula (VIII) with Grignard compounds of the general formula (IX) according
to the
following reaction equation 1 (RE 1), where R17 in the formulae (IX) and (I)
is as defined
above for R11, R12, R13, Kr-,14,
the preferences applying correspondingly. For R15 and R16 in
formula (VIII), the definitions and preferences given for the phosphine ligand
(I) apply
correspondingly.
CI R17
R17 /
R15 R1-5P
+ 4 R17MgC1 _____ 1. + 4 MgC12
Ris Fos
CI ci R17 R17
VIII IX I
RE 1
The general reaction of 1 ,2-bis(dichlorophosphino)ethane with a butyl
Grignard compound
is described in Jack Lewis, et al. Journal of Organometallic Chemistry, 433
(1992), 135 ¨
139.
Phosphine ligands of the general formula (I) in which n and m are both 0 and
in which R11,
R12, R13 and R14 are each independently unsubstituted or at least
monosubstituted -C12-
C30-alkyl are additionally obtainable, for example, by reaction of 1,2-
bis(dihydrophosphino)ethane compounds of the general formula (X) with terminal
olefins of
the general formula (XI) according to the following reaction equation 2 (RE
2), where, for
R18 in the formulae (XI) and (I), the definitions and preferences given above
for R11, R12,
14 ¨
R13, K apply analogously. For R15 and R16 in formula (X), the definitions and
preferences
given for the phosphine ligand (I) apply correspondingly.
CA 02854047 2014-04-30
18
R15 PH R15 PqCF12)3R18)2
R pH
= -2 R16 P((CH2)3R18)2
X XI
RE 2
The general reaction of 1,2-bis(dihydrophosphino)ethane with a terminal olefin
(CH2=CHCH2-0CH3) is described in Warren K. Miller, et al. Inorganic Chemistry
2002, 41,
5453 ¨ 5465.
The phosphine ligands (I) in which n and m are both 0 are additionally
obtainable, for
example, by reaction of monophosphine compounds of the general formula (XII)
with
alkyne compounds of the general formula (XIII) according to the following
reaction
equation 3 (RE 3), where R17 in the formulae (XII) and (I) is as defined above
for R11, R12,
R13, R14,
the preferences applying correspondingly. For R15 and R16 in formula (XIII),
the
definitions and preferences given for the phosphine ligand (I) apply
correspondingly.
,, R17
R1P
2 (R17)2PH +
,,/s\
R16
R17 R17
15 XII XIII
RE 3
The general reaction of monophosphine compounds with alkyne compounds is
described
in US 3,681,481.
In a particularly preferred embodiment, the transition metal complexes used as
catalysts
comprise one (1) bidentate phosphine ligand of the general formula (I) and at
least one
monodentate monophosphine ligand with at least one organic radical having 1 to
20
carbon atoms.
Denticity is understood in the context of the present invention to mean the
number of
bonds that the phosphine ligand can form to the central transition metal atom
from one
phosphorus atom of the phosphine ligand. In other words, monodentate phosphine
ligands
can form one bond from the phosphorus atom to the central transition metal
atom;
CA 02854047 2014-04-30
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bidentate phosphine ligands can form two bonds from the phosphorus atoms to
the central
transition metal atom.
Preferred monodentate monophosphine ligands are monophosphine ligands of the
general
formula (la)
pR19R20R21 (la)
in which
R19, R20, R21 are each independently unsubstituted or at least monosubstituted
-C1-C20-
alkyl, -phenyl, -benzyl, -cyclohexyl or -(CH2)-cyclohexyl,
where the substituents are selected from the group consisting of -C1-C20-
alkyl, -F, -Cl, -Br, -OH, -0Ra, -COOH, -COORa, -000Ra, -CN, -NH2, -N(Ra)2
and -NHRa;
Ra is -C1-C4-alkyl.
The -C1-C20-alkyl may be linear or branched. Suitable radicals for R19, R20, =-
.21
K include, for
example, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 1-(2-methyl)propyl, 2-(2-
methyl)propyl,
1-pentyl, 1-hexyl, 1-heptyl, 1-octyl, 1-nonyl, 1-decyl, 1-undecyl, 1-dodecyl,
1-tridecyl, 1-
tetradecyl, 1-pentadecyl, 1-hexadecyl, 1-heptadecyl, 1-octadecyl, 1-nonadecyl,
1-eicosyl,
cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl, methylcyclopentyl,
methylcyclohexyl,
1-(2-methyl)pentyl, 1-(2-ethyl)hexyl, 1-(2-propyl)heptyl and norbomyl.
Preference is given to monodentate monophosphine ligands (la) in which the
three R19,
R20, K,-.21
radicals are the same. Particular preference is given to monodentate
monophosphine ligands (la) of the formula P(n-CqH2q.1)3 where q is 1 to 20,
especially
where q is 1 to 12. Most preferably, the monodentate monophosphine ligand (la)
is
selected from the group consisting of tri-n-butylphosphine, tri-n-
hexylphosphine, tri-n-
octylphosphine, tri-n-decylphosphine and tri-n-dodecylphosphine.
The transition metal complex used as a catalyst preferably comprises one
bidentate
phosphine ligand (I) and two monodentate monophosphine ligands (la), where the
definitions and preferences given for the bidentate phosphine ligands (I) and
the
monodentate monophosphine ligands (la) apply correspondingly.
The transition metal complex may further comprise further ligands, examples of
which
include hydride, fluoride, chloride, bromide, iodide, formate, acetate,
propionate,
carboxylate, acetylacetonate, carbonyl, DMSO, hydroxide, trialkylamine,
alkoxide.
CA 02854047 2014-04-30
The transition metal complexes used as catalysts can be produced either
directly in their
active form or proceeding from customary standard complexes, for example [M(p-
cymene)C12]2, [M(benzene)C12], [M(COD)(allyI)], [MCI3 x H20],
[M(acetylacetonate)3],
5 [M(COD)C12]2, [M(DMS0)4C12] where M is an element from group 8, 9 or 10
of the Periodic
Table, with addition of the corresponding phosphine ligand(s) only under
reaction
conditions in process stage (a) (in situ).
In the process according to the invention, the catalyst used is preferably at
least one
20 [Ru(Pnhexy13)2(1,2-bis(dihexadecylphosphino)ethane)(H)2],
[Ru(Pnocty13)2(1,2-bis(dihexadecylphosphino)ethane)(F)2],
[Ru(P"decy13)2(1,2-bis(dihexadecylphosphino)ethane)(1-1)21,
[Ru(PnBu3)2(1,2-bis(dioctadecylphosphino)ethane))(H)21,
[Ru(Pnhexy13)2(1,2-bis(dioctadecylphosphino)ethane)(H)2],
[Ru(Pndecy13)(1,2-bis(ditetradecylphosphino)ethane)(C0)(H)2],
[Ru(PnBu3)(1,2-bis(dipentadecylphosphino)ethane)(C0)(H)2],
[Ru(Pnhexy13)(1,2-bis(dipentadecylphosphino)ethane)(C0)(H)2],
[Ru(Pnocty13)(1,2-bis(dipentadecylphosphino)ethane)(C0)(H)2],
[Ru(Pndecy13)(1,2-bis(dipentadecylphosphino)ethane)(C0)(H)2],
[Ru(PnBu3)(1,2-bis(dihexadecylphosphino)ethane)(C0)(H)2],
[Ru(Pnhexy13)(1,2-bis(dihexadecylphosphino)ethane)(C0)(1-)2],
[Ru(Pnocty13)(1,2-bis(dihexadecylphosphino)ethane)(C0)(H)2],
[Ru(P"decy13)(1,2-bis(dihexadecylphosphino)ethane)(C0)(H)2],
[Ru(PnBu3)(1,2-bis(dioctadecylphosphino)ethane)(C0)(H)2],
[Ru(Pnhexy13)(1,2-bis(dioctadecylphosphino)ethane))(C0)(H)2],
CA 02854047 2014-04-30
21
[Ru(Pnocty13)(1,2-bis(dioctadecylphosphino)ethane)(CO(H)21
[Ru(Pndecy13)(1,2-bis(dioctadecylphosphino)ethane)(C0)(H)2],
[Ru(PnBu3)(1,2-bis(ditetradecylphosphino)ethane)(C0)(H)(HC00)],
[Ru(Pnhexy13)(1,2-bis(ditetradecylphosphino)ethane)(C0)(H)(HC00)],
[Ru(Pnocty13) (1,2-bis(ditetradecylphosphino)ethane)(C0)(H)(HC00)],
[Ru(Pnclecy13)(1,2-bis(ditetradecylphosphino)ethane)(C0)(H)(HC00)],
[Ru(PnBu3)(1,2-bis(dipentadecylphosphino)ethane)(C0)(H)(HC00)],
[Ru(Pnhexy13)(1,2-bis(dipentadecylphosphino)ethane)(C0)(H)(HC00)],
[Ru(Pnocty13)(1,2-bis(dipentadecylphosphino)ethane)(C0)(H)(HC00)],
[Ru(Pnclecy13)(1,2-bis(dipentadecylphosphino)ethane)(C0)(H)(HC00)],
[Ru(PnBu3)(1,2-bis(dihexadecylphosphino)ethane)(C0)(H)(HC00)],
[Ru(Pnhexy13)(1,2-bis(dihexadecylphosphino)ethane)(C0)(H)(HC00)],
[Ru(Pnocty13)(1,2-bis(dihexadecylphosphino)ethane)(C0)(H)(HC00)],
[Ru(Pndecy13)(1,2-bis(dihexadecylphosphino)ethane)(C0)(H)(HC00)],
[Ru(PnBu3)(1,2-bis(dioctadecylphosphino)ethane)(C0)(H)(HC00)],
[Ru(Pnhexy13)(1,2-bis(dioctadecylphosphino)ethane))(C0)(H)(HC00)],
[Ru(Pnocty13)(1,2-bis(dioctadecylphosphino)ethane)(CO(H)(HC00)] and
[Ru(Pndecy13)(1,2-bis(dioctadecylphosphino)ethane)(C0)(H)(HC00)].
With these, it is possible in the hydrogenation of carbon dioxide to achieve
TOF values
(turnover frequencies) of greater than 1000 h-1 and partition coefficients PK
greater than
100.
"Homogeneously catalyzed" is understood in the context of the present
invention to mean
that the catalyst is present at least partly dissolved in the liquid reaction
medium. In a
preferred embodiment, at least 90% of the catalyst used in process stage (a)
is present
dissolved in the liquid reaction medium, more preferably at least 95%,
especially
preferably more than 99%, the catalyst most preferably being present
completely dissolved
in the liquid reaction medium (100%), based in each case on the total amount
of the
catalyst present in the liquid reaction medium (liquid phases of the reaction
mixture (Rg)).
The amount of the metal component in the transition metal complex used as the
catalyst in
process stage (a) is generally 0.1 to 5000 ppm by weight, preferably 1 to 800
ppm by
weight and especially preferably 5 to 800 ppm by weight, based in each case on
the
overall liquid reaction mixture (Rg) in the hydrogenation reactor. The
catalyst is preferably
selected such that it is present enriched in the upper phase (U1), which means
that the
upper phase (U1) comprises the majority of the catalyst. "Enriched" and
"majority" with
regard to the catalyst are understood in the context of the present invention
to mean a
partition coefficient of the catalyst PK = [concentration of the catalyst in
the upper phase
(U1)] / [concentration of the catalyst in the lower phase (L1)] of ?_ 10.
Preference is given to
CA 02854047 2014-04-30
22
a partition coefficient PK of 50 and particular preference to a partition
coefficient PK of
100.
With the transition metal complexes used as catalysts, it is possible in the
hydrogenation
of carbon dioxide to achieve TOF values (turnover frequencies) of greater than
1000 h-1.
(TON = mol of formic acid-amine adduct (A2) per mole of metal component in the
catalyst
based on the reaction time; TOF = mol of formic acid-amine adduct (A2) per
mole of metal
component in the catalyst per 1 hour of reaction time.) Turnover frequency
(TOF) and
turnover number TON; for definition of TOF and TON see: J.F. Hartwig,
Organotransition
Metal Chemistty, 1st edition, 2010, University Science Books,
Sausalito/California p. 545).
The present invention therefore also provides the transition metal complex and
for the use
thereof as a catalyst, especially as a catalyst in a process for preparing
formic acid.
The present invention thus also provides a transition metal complex comprising
at least
one element selected from groups 8, 9 and 10 of the Periodic Table and at
least one
phosphine ligand of the general formula (I).
The present invention thus also provides a transition metal complex comprising
a
phosphine ligand of the general formula (I) and at least one monodentate
phosphine ligand
of the general formula (la).
The present invention thus also provides for the use of the transition metal
complex as a
catalyst in a process for preparing formic acid.
The hydrogenation of carbon dioxide in process stage (a) is effected in the
liquid phase,
preferably at a temperature in the range from 20 to 200 C and a total pressure
in the range
from 0.2 to 30 MPa abs. The temperature is preferably at least 30 C and
especially
preferably at least 40 C, and preferably at most 150 C, especially preferably
at most
120 C and very especially preferably at most 80 C. The total pressure is
preferably at
least 1 MPa abs and especially preferably at least 5 MPa abs, and preferably
at most 20
MPa abs.
In a preferred embodiment, the hydrogenation in process stage (a) is effected
at a
temperature in the range from 40 to 80 C and a pressure in the range from 5 to
20 MPa
abs.
The partial pressure of carbon dioxide in process stage (a) is generally at
least 0.5 MPa
and preferably at least 2 MPa, and generally at most 8 MPa. In a preferred
embodiment,
CA 02854047 2014-04-30
23
the hydrogenation in process stage (a) is effected at a partial pressure of
carbon dioxide in
the range from 2 to 7.3 MPa.
The partial pressure of hydrogen in process stage (a) is generally at least
0.5 MPa and
preferably at least 1 MPa, and generally at most 25MPa and preferably at most
15 MPa. In
a preferred embodiment, the hydrogenation in process stage (a) is effected at
a partial
pressure of hydrogen in the range from 1 to 15 MPa.
The molar ratio of hydrogen to carbon dioxide in the reaction mixture (Rg) in
the
hydrogenation reactor is preferably 0.1 to 10 and especially preferably 1 to
3.
The molar ratio of carbon dioxide to tertiary amine (Al) in the reaction
mixture (Rg) in the
hydrogenation reactor is preferably 0.1 to 10 and especially preferably 0.5 to
3.
The hydrogenation reactors used may in principle be any reactors which are
suitable for
gas/liquid reactions under the given temperature and the given pressure.
Suitable
standard reactors for gas-liquid reaction systems are specified, for example,
in K. D.
Henkel, "Reactor Types and Their Industrial Applications", in Ullmann's
Encyclopedia of
Industrial Chemistry, 2005,. Wiley-VCH Verlag GmbH & Co. KGaA, DOI:
10.1002/14356007.b04_087, chapter 3.3 "Reactors for gas-liquid reactions".
Examples
include stirred tank reactors, tubular reactors or bubble column reactors.
The hydrogenation of carbon dioxide in the process according to the invention
can be
performed batchwise or continuously. In batchwise mode, the reactor is charged
with the
desired liquid and any solid feedstocks and auxiliaries, and then carbon
dioxide and the
polar solvent are injected to the desired pressure at the desired temperature.
After the end
of the reaction, the reactor is generally decompressed and the two liquid
phases formed
are separated from one another. In continuous mode, the feedstocks and
auxiliaries,
including the carbon dioxide and the hydrogen, are added continuously. In a
corresponding manner, the liquid phases are removed continuously from the
reactor, such
that the liquid level in the reactor remains constant on average. Preference
is given to the
continuous hydrogenation of carbon dioxide.
The mean residence time of the components present in the reaction mixture (Rg)
in the
hydrogenation reactor is generally 5 minutes to 5 hours.
In the homogeneously catalyzed hydrogenation, in process stage (a), a
hydrogenation
mixture (H) is obtained which comprises the catalyst, the polar solvent, the
tertiary amine
(Al) and the at least one formic acid-amine adduct (A2).
CA 02854047 2014-04-30
24
"Formic acid-amine adduct (A2)" is understood in the context of the present
invention to
mean either one (1) formic acid-amine adduct (A2) or mixtures of two or more
formic acid-
amine adducts (A2). Mixtures of two or more formic acid-amine adducts (A2) are
obtained
in process stage (a) when two or more tertiary amines (Al) are used in the
reaction
mixture (Rg) used.
In a preferred embodiment of the process according to the invention, a
reaction mixture
(Rg) is used in process stage (a) which comprises one (1) tertiary amine (Al)
to obtain a
hydrogenation mixture (H) comprising one (1) formic acid-amine adduct (A2).
In a particularly preferred embodiment of the process according to the
invention, in
process stage (a), a reaction mixture (Rg) is used which comprises, as the
tertiary amine
(Al), tri-n-hexylamine to obtain a hydrogenation mixture (H) which comprises
the formic
acid-amine adduct of tri-n-hexylamine and formic acid and corresponds to the
following
formula (A3)
N(n-hexy1)3* x, HCOOH (A3).
In the formic acid-amine adduct of the general formula (A2), the R1, R2, R3
radicals are
each as defined above for the tertiary amine of the formula (Al), where the
preferences
mentioned there apply correspondingly.
In the general formulae (A2) and (A3), xi is in the range from 0.4 to 5. The
factor x, gives
the averaged composition of the formic acid-amine adduct (A2) or (A3), i.e.
the ratio of
bound tertiary amine (Al) to bound formic acid in the formic acid-amine adduct
(A2) or
(A3).
The factor xi can be determined, for example, by determining the formic acid
content by
acid-base titration with an alcoholic KOH solution using phenolphthalein. In
addition, it is
possible to determine the factor xi by determining the amine content by gas
chromatography. The exact composition of the formic acid-amine adduct (A2) or
(A3)
depends on many parameters, for example the concentrations of formic acid and
tertiary
amine (Al), the pressure, the temperature and the presence and nature of
further
components, especially of the polar solvent.
Therefore, the composition of the formic acid-amine adduct (A2) or (A3), i.e.
the factor xõ
can also vary over the individual process stages. For example, after removal
of the polar
solvent, a formic acid-amine adduct (A2) or (A3) with a relatively high formic
acid content
generally forms, the excess bound tertiary amine (Al) being released from the
formic acid-
amine adduct (A2) and forming a secondary phase.
CA 02854047 2014-04-30
In process stage (a), a formic acid-amine adduct (A2) or (A3) is generally
obtained in
which x, is in the range from 0.4 to 5, preferably in the range from 0.7 to
1.6.
5 The formic acid-amine adduct (A2) is present enriched in the lower phase
(L1), i.e. the
lower phase (L1) comprises the majority of the formic acid-amine adduct (A2).
"Enriched"
or "majority" with regard to the formic acid-amine adduct (A2) should be
understood in the
context of the present invention to mean a proportion by weight of the formic
acid-amine
adduct (A2) in the lower phase (L1) of > 50% based on the total weight of the
formic acid-
10 amine adduct (A2) in the liquid phases (upper phase (U1) and lower phase
(L1)) in the
hydrogenation reactor.
Preferably, the proportion by weight of the formic acid-amine adduct (A2) in
the lower
phase (L1) is > 70%, especially > 90%, based in each case on the total weight
of the
15 formic acid-amine adduct (A2) in the upper phase (U1) and the lower
phase (L1).
Workup of the hydrogenation mixture (H); process stage (b)
The hydrogenation mixture (H) obtained in the hydrogenation of carbon dioxide
in process
20 stage (a) preferably has two liquid phases, optionally after addition of
water, and is
subjected to further workup in process stage (b) according to one of steps
(b1), (b2) or
(b3).
Workup according to process stage (b1)
In a preferred embodiment, the hydrogenation mixture (H) is subjected to
further workup
according to step (b1).
In this case, the hydrogenation mixture (H) obtained in process stage (a) is
subjected to
complex used as the catalyst compared to the prior art, the removal of the
catalyst by
phase separation is very substantially complete. The amount of the metal
component of
the catalyst present in the lower phase (L1) is generally less than 4 ppm by
weight,
preferably less than 3 ppm by weight, more preferably less than 2 ppm by
weight and
CA 02854047 2014-04-30
26
especially preferably less than or equal to 1 ppm by weight, based in each
case on the
lower phase (L1).
Residues of the catalyst can optionally be depleted further from the lower
phase (L1) by
subsequent extraction (workup according to process stage b3). Due to the
distinct
improvement in the partition coefficient (PK), the removal of the transition
metal compound
used as the catalyst by phase separation is very substantially complete, and
so it is
possible to dispense with a subsequent extraction.
In a preferred embodiment, the upper phase (U1) is recycled to the
hydrogenation reactor.
The lower phase (L1), in a preferred embodiment, is supplied to the first
distillation
apparatus in process stage (c). It may also be advantageous to recycle any
further liquid
phase comprising unconverted carbon dioxide and present above the two liquid
phases,
and any gas phase comprising unconverted carbon dioxide and/or unconverted
hydrogen,
to the hydrogenation reactor. It may be desirable, for example, to discharge
unwanted by-
products or impurities by discharging a portion of the upper phase (U1) and/or
a portion of
the liquid or gaseous phases comprising carbon dioxide or carbon dioxide and
hydrogen
from the process.
The hydrogenation mixture (H) obtained in process stage (a) is generally
separated by
gravimetric phase separation. Suitable phase separation apparatuses are, for
example,
standard apparatuses and standard methods which can be found, for example, in
E. Muller
et al., "Liquid-liquid Extraction", in Ullman's Encyclopedia of Industrial
Chemistry, 2005,
Wiley-VCH Verlag GmbH & Co. KGaA, DOI: 10.1002/14356007.b93_06, chapter 3
"Apparatus".
The phase separation can be effected, for example, after decompression to
about or close
to atmospheric pressure and cooling of the liquid hydrogenation mixture, for
example to
about or close to ambient temperature.
In the context of the present invention, it has been found that, in the
present system, i.e. a
lower phase (L1) enriched with the formic acid-amine adducts (A2) and the
polar solvent,
and an upper phase (U1) enriched with the tertiary amine (Al) and the
catalyst, the two
liquid phases can also be separated from one another very efficiently even
under a
distinctly elevated pressure. Therefore, in the process according to the
invention, the polar
solvent and the tertiary amine (Al) are selected such that the separation of
the lower
phase (L1) enriched with the formic acid-amine adducts (A2) and the polar
solvent from
the upper phase (U1) enriched with tertiary amine (Al) and catalyst, and the
recycling of
the upper phase (U1) to the hydrogenation reactor, can be performed at a
pressure of 1 to
30 MPa abs. According to the total pressure in the hydrogenation reactor, the
pressure is
CA 02854047 2014-04-30
27
preferably at most 20 MPa abs. Thus, it is possible, without prior
decompression, to
separate the two liquid phases (upper phase (U1) and lower phase (L1)) from
one another
in the first phase separation apparatus, and to recycle the upper phase (U1)
to the
hydrogenation reactor without a significant pressure increase.
It is also possible to perform the phase separation directly in the
hydrogenation reactor. In
this embodiment, the hydrogenation reactor simultaneously functions as the
first phase
separation apparatus, and process stages (a) and (b1) are both performed in
the
hydrogenation reactor. In this case, the upper phase (U1) remains in the
hydrogenation
reactor and the lower phase (L1) is supplied to the first distillation
apparatus in process
stage (c).
In one embodiment, the process according to the invention is performed in such
a way that
the pressure and the temperature in the hydrogenation reactor and in the first
phase
separation apparatus are the same or approximately the same, "approximately
the same"
being understood in the present case to mean a pressure difference of up to +1-
0.5 MPa
or a temperature difference of up to +/-10 C.
It has also been found that, surprisingly, in the present system, both liquid
phases (upper
phase (U1) and lower phase (L1)) can also be separated very efficiently from
one another
at elevated temperature, which corresponds to the reaction temperature in the
hydrogenation reactor. In this respect, for phase separation in process stage
(b1), there is
also no requirement for cooling and subsequent heating of the upper phase (U1)
to be
recycled, which likewise saves energy.
Workup according to process stage (b3)
In a further preferred embodiment, the hydrogenation mixture (H) is subjected
to further
workup according to step (b3).
In this case, the hydrogenation mixture (H) obtained in process stage (a), as
described
above for process stage (b1), is separated in the first phase separation
apparatus into the
lower phase (L1) and the upper phase (U1), which is recycled to the
hydrogenation
reactor. In relation to the phase separation, the details and preferences
given for process
stage (b1) apply correspondingly to process stage (b3). In the case of the
workup
according to step (b3) too, it is possible to conduct the phase separation
directly in the
hydrogenation reactor. In this embodiment, the hydrogenation reactor
simultaneously
functions as the first phase separation apparatus. In that case, the upper
phase (U1)
remains in the hydrogenation reactor and the lower phase (L1) is supplied to
the extraction
unit.
CA 02854047 2014-04-30
28
The lower phase (L1) obtained after phase separation is subsequently subjected
in an
extraction unit to an extraction with a tertiary amine (Al) as an extractant
for removal of
the residues of the catalyst to obtain a raffinate (R2) comprising the formic
acid-amine
adduct (A2) and the at least one polar solvent, and an extract (E2) comprising
the tertiary
amine (Al) and the residues of the catalyst.
In a preferred embodiment, the extractant used is the same tertiary amine (Al)
present in
the reaction mixture (Rg) in process stage (a), such that the details and
preferences given
for process stage (a) in relation to the tertiary amine (Al) apply
correspondingly to process
stage (b3).
The extract (E2) obtained in process stage (b3), in a preferred embodiment, is
recycled to
the hydrogenation reactor in process stage (a). This enables efficient
recovery of the
catalyst. The raffinate (R2), in a preferred embodiment, is supplied to the
first distillation
apparatus in process stage (c).
Preferably, the extractant used in process stage (b3) is the tertiary amine
(Al) which is
obtained in the thermal dissociation unit in process stage (e). In a preferred
embodiment,
the tertiary amine (Al) obtained in the thermal dissociation unit in process
stage (e) is
recycled to the extraction unit in process stage (b3).
The extraction in process stage (b3) is effected generally at temperatures in
the range
from 0 to 150 C, preferably in the range from 30 to 100 C, and pressures in
the range from
0.1 to 8 MPa. The extraction can also be performed under hydrogen pressure.
The extraction of the catalyst can be performed in any suitable apparatus
known to those
skilled in the art, preferably in countercurrent extraction columns, mixer-
settler cascades or
combinations of mixer-settler cascades and countercurrent extraction columns.
It may be the case that, as well as the catalyst, proportions of individual
components of the
polar solvent from the lower phase (L1) to be extracted are also dissolved in
the
extractant, the tertiary amine (Al). This is not a disadvantage for the
process, since the
amount of polar solvent already extracted need not be supplied to the solvent
removal,
and hence vaporization energy is saved under some circumstances.
Workup according to process stage (b2)
In a further preferred embodiment, the hydrogenation mixture (H) is subjected
to further
workup according to step (b2).
CA 02854047 2014-04-30
29
In this case, the hydrogenation mixture (H) obtained in process stage (a) is
supplied
entirely, without prior phase separation, directly to the extraction unit. In
relation to the
extraction, the details and preferences given for process stage (b3) apply
correspondingly
to process stage (b2).
In this case, the hydrogenation mixture (H) is subjected in an extraction unit
to an
extraction with a tertiary amine (Al) as an extractant for removal of the
catalyst to obtain a
raffinate (R1) comprising the formic acid-amine adduct (A2) and the at least
one polar
solvent, and an extract (El) comprising the tertiary amine (Al) and the
catalyst.
In a preferred embodiment, the extractant used is the same tertiary amine (Al)
present in
the reaction mixture (Rg) in process stage (a), such that the details and
preferences given
for process stage (a) in relation to the tertiary amine (Al) apply
correspondingly to process
stage (b2).
The extract (El) obtained in process stage (b2), in a preferred embodiment, is
recycled to
the hydrogenation reactor in process stage (a). This enables efficient
recovery of the
catalyst. The raffinate (R1), in a preferred embodiment, is supplied to the
first distillation
apparatus in process stage (c).
Preferably, the extractant used in process stage (b2) is the tertiary amine
(Al) which is
obtained in the thermal dissociation unit in process stage (e). In a preferred
embodiment,
the tertiary amine (Al) obtained in the thermal dissociation unit in process
stage (e) is
recycled to the extraction unit in process stage (b2).
The extraction in process stage (b2) is effected generally at temperatures in
the range
from 0 to 150 C, preferably in the range from 30 to 100 C, and pressures in
the range from
0.1 to 8 MPa. The extraction can also be performed under hydrogen pressure.
The extraction of the catalyst can be performed in any suitable apparatus
known to those
skilled in the art, preferably in countercurrent extraction columns, mixer-
settler cascades or
combinations of mixer-settler cascades and countercurrent extraction columns.
It may be the case that, as well as the catalyst, proportions of individual
components of the
polar solvent from the hydrogenation mixture (H) to be extracted are also
dissolved in the
extractant, the tertiary amine (Al). This is not a disadvantage for the
process, since the
amount of polar solvent already extracted need not be supplied to the solvent
removal,
and hence vaporization energy is saved under some circumstances.
Removal of the polar solvent: process stage (c)
CA 02854047 2014-04-30
In process stage (c), the polar solvent is removed from lower phase (L1), from
the raffinate
(R1) or from the raffinate (R2) in a first distillation apparatus. In the
first distillation
apparatus, a distillate (D1) and a biphasic bottoms mixture (B1) are obtained.
The distillate
5 (D1) comprises the polar solvent removed and, in a preferred embodiment,
is recycled into
the hydrogenation reactor in step (a). The bottoms mixture (B1) comprises the
upper
phase (U2) comprising the tertiary amine (Al), and the lower phase (L2)
comprising the
formic acid-amine adduct (A2). In one embodiment of the process according to
the
invention, in the first distillation apparatus, in process stage (c), the
polar solvent is partly
10 removed, and so the bottoms mixture (B1) comprises as yet unremoved
polar solvent. In
process stage (c), it is possible to remove, for example, 5 to 98% by weight
of the polar
solvent present in the lower phase (L1), in the raffinate (R1) or in the
raffinate (R2),
preferably 50 to 98% by weight, more preferably 80 to 98% by weight and
especially
preferably 80 to 90% by weight, based in each case on the total weight of the
polar solvent
15 present in the lower phase (L1), in the raffinate (R1) or in the
raffinate (R2).
In a further embodiment of the process according to the invention, in the
first distillation
apparatus, in process stage (c), the polar solvent is completely removed.
"Completely
removed" is understood in the context of the present invention to mean a
removal of more
20 than 98% by weight of the polar solvent present in the lower phase (L1),
in the raffinate
(R1) or in the raffinate (R2), preferably more than 98.5% by weight,
especially preferably
more than 99% by weight, especially more than 99.5% by weight, based in each
case on
the total weight of the polar solvent present in the lower phase (L1), in the
raffinate (R1) or
in the raffinate (R2).
The distillate (D1) removed in the first distillation apparatus, in a
preferred embodiment, is
recycled to the hydrogenation reactor in step (a).
The polar solvent can be removed from the lower phase (L1), the raffinate (R1)
or the
raffinate (R2), for example, in an evaporator or in a distillation unit
consisting of evaporator
and column, the column being filled with structured packings, random packings
and/or
trays.
The at least partial removal of the polar solvent is effected preferably at a
bottom
temperature at which, at the given pressure, no free formic acid is formed
from the formic
acid-amine adduct (A2). The factor x, of the formic acid-amine adduct (A2) in
the first
distillation apparatus is generally in the range from 0.4 to 3, preferably in
the range from
0.6 to 1.8, especially preferably in the range from 0.7 to 1.7.
CA 02854047 2014-04-30
31
In general, the bottom temperature in the first distillation apparatus is at
least 20 C,
preferably at least 50 C and especially preferably at least 70 C, and
generally at most
210 C, preferably at most 190 C. The temperature in the first distillation
apparatus is
generally in the range from 20 C to 210 C, preferably in the range from 50 C
to 190 C.
The pressure in the first distillation apparatus is generally at least 0.001
MPa abs,
preferably at least 0.005 MPa abs and especially preferably at least 0.01 MPa
abs, and
generally at most 1 MPa abs and preferably at most 0.1 MPa abs. The pressure
in the first
distillation apparatus is generally in the range from 0.0001 MPa abs to 1 MPa
abs,
preferably in the range from 0.005 MPa abs to 0.1 MPa abs and especially
preferably in
the range from 0.01 MPa abs to 0.1 MPa abs.
In the removal of the polar solvent in the first distillation apparatus, the
formic acid-amine
adduct (A2) and free tertiary amine (Al) may occur in the bottoms of first
distillation
apparatus, since the removal of the polar solvent gives rise to formic acid-
amine adducts
(A2) with relatively low amine content. This forms a bottoms mixture (B1)
comprising the
formic acid-amine adduct (A2) and the free tertiary amine (Al). The bottoms
mixture (B1)
comprises, depending on the amount of the polar solvent removed, the formic
acid-amine
adduct (A2) and possibly the free tertiary amine (Al) formed in the bottoms of
the first
distillation apparatus. The bottoms mixture (B1) is optionally subjected to
further workup in
process stage (d) for further workup, and then supplied to process stage (e).
It is also
possible to supply the bottoms mixture (B1) from process stage (c) directly to
process
stage (e).
In process stage (d), the bottoms mixture (B1) obtained in step (c) can be
separated in a
second phase separation apparatus into the upper phase (U2) and the lower
phase (L2).
The lower phase (L2) is subsequently subjected to further workup according to
process
stage (e). In a preferred embodiment, the upper phase (U2) from the second
phase
separation apparatus is recycled to the hydrogenation reactor in step (a). In
a further
preferred embodiment, the upper phase (U2) from the second phase separation
apparatus
is recycled to the extraction unit. For process stage (d) and the second phase
separation
apparatus, the details and preferences for the first phase separation
apparatus apply
correspondingly.
In one embodiment, the process according to the invention thus comprises steps
(a), (b1),
(c), (d) and (e). In a further embodiment, the process according to the
invention comprises
steps (a), (b2), (c), (d) and (e). In a further embodiment, the process
according to the
invention comprises steps (a), (b3), (c), (d) and (e). In a further
embodiment, the process
according to the invention comprises steps (a), (b1), (c) and (e). In a
further embodiment,
the process according to the invention comprises steps (a), (b2), (c) and (e).
In a further
embodiment, the process according to the invention comprises steps (a), (b3),
(c) and (e).
CA 02854047 2014-04-30
32
In one embodiment, the process according to the invention consists of steps
(a), (b1), (c),
(d) and (e). In a further embodiment, the process according to the invention
consists of
steps (a), (b2), (c), (d) and (e). In a further embodiment, the process
according to the
invention consists of steps (a), (b3), (c), (d) and (e). In a further
embodiment, the process
according to the invention consists of steps (a), (b1), (c) and (e). In a
further embodiment,
the process according to the invention consists of steps (a), (b2), (c) and
(e). In a further
embodiment, the process according to the invention consists of steps (a),
(b3), (c) and (e).
Dissociation of the formic acid-amine adduct (A2); process staqe (e)
The bottoms mixture (B1) obtained according to step (c), or the lower phase
(L2) obtained,
optionally after the workup according to step (d), is supplied to a thermal
dissociation unit
for further conversion.
The formic acid-amine adduct (A2) present in the bottoms mixture (B1) and/or
possibly in
the lower phase (L2) is dissociated in the thermal dissociation unit to formic
acid and the
corresponding tertiary amine (Al).
The formic acid is discharged from the thermal dissociation unit. The tertiary
amine (Al) is
recycled to the hydrogenation reactor in step (a). The tertiary amine (Al)
from the thermal
dissociation reactor can be recycled directly to the hydrogenation reactor. It
is also
possible to recycle the tertiary amine (Al) from the thermal dissociation unit
first to the
extraction unit in process stage (b2) or process stage (b3) and then to pass
it onward from
the extraction unit to the hydrogenation reactor in step (a); this embodiment
is preferred.
In a preferred embodiment, the thermal dissociation unit comprises a second
distillation
apparatus and a third phase separation apparatus, the formic acid-amine adduct
(A2)
being dissociated in the second distillation apparatus to obtain a distillate
(D2) which
comprises formic acid and is discharged (withdrawn) from the second
distillation
apparatus, and a biphasic bottoms mixture (B2) comprising an upper phase (U3),
which
comprises the tertiary amine (Al), and a lower phase (L3), which comprises the
formic
acid-amine adduct (A2).
The formic acid obtained in the second distillation apparatus can be withdrawn
from the
second distillation apparatus, for example, (i) overhead, (ii) overhead and
via a side draw
or (iii) only via a side draw. When the formic acid is withdrawn overhead,
formic acid is
obtained with a purity of up to 99.99% by weight. In the case of withdrawal
via a side draw,
aqueous formic acid is obtained, in which case particular preference is given
here to a
mixture comprising about 85% by weight of formic acid. According to the water
content of
CA 02854047 2014-04-30
33
the bottoms mixture (B1) supplied to the thermal dissociation unit or
optionally to the lower
phase (L2), the formic acid can be withdrawn to an enhanced degree as the top
product,
or to an enhanced degree via the side draw. If required, it is also possible
to withdraw .
formic acid only via the side draw, preferably with a formic acid content of
about 85% by
weight, in which case the amount of water required can optionally also be
established by
adding additional water to the second distillation apparatus. The thermal
dissociation of the
formic acid-amine adduct (A2) is effected generally according to process
parameters
known from the prior art with regard to pressure, temperature and apparatus
configuration.
These are described, for example, in EP 0 181 078 or WO 2006/021 411. Suitable
second
distillation apparatuses are, for example, distillation columns, which
generally comprise
random packings, structured packings and/or trays.
In general, the bottom temperature in the second distillation apparatus is at
least 130 C,
preferably at least 140 C and especially preferably at least 150 C, and
generally at most
210 C, preferably at most 190 C, especially preferably at most 185 C. The
pressure in the
second distillation apparatus is generally at least 1 hPa abs, preferably at
least 50 hPa abs
and especially preferably at least 100 hPa abs, and generally at most 500 hPa,
especially
preferably at most 300 hPa abs and especially preferably at most 200 hPa abs.
The bottoms mixture (82) obtained in the bottom of the second distillation
apparatus is
biphasic. In a preferred embodiment, the bottoms mixture (B2) is supplied to
the third
phase separation apparatus of the thermal dissociation unit and separated
there into the
upper phase (U3), which comprises the tertiary amine (Al), and the lower phase
(L3),
which comprises the formic acid-amine adduct (A2). The upper phase (U3) is
discharged
from the third phase separation apparatus of the thermal dissociation unit and
recycled to
the hydrogenation reactor in step (a). The recycling can be effected directly
to the
hydrogenation reactor in step (a), or the upper phase (U3) is supplied first
to the extraction
unit in step (b2) or step (b3) and passed onward thence to the hydrogenation
reactor in
step (a). The lower phase (L3) obtained in the third phase separation
apparatus is then
supplied again to the second distillation apparatus of the thermal
dissociation unit. The
formic acid-amine adduct (A2) present in the lower phase (L3) is then
subjected in the
second distillation apparatus to another dissociation to again obtain formic
acid and free
tertiary amine (Al) and to form, in the bottom of the second distillation
apparatus of the
thermal dissociation unit, another biphasic bottoms mixture (B2), which is
then supplied
again to the third phase separation apparatus of the thermal dissociation unit
for further
workup.
The bottoms mixture (81) and/or optionally the lower phase (L2) can be
supplied to the
thermal dissociation unit in process stage (e) in the second distillation
apparatus and/or
the third phase separation apparatus. In a preferred embodiment, the bottoms
mixture (81)
CA 02854047 2014-04-30
34
and/or optionally the lower phase (L2) is fed into the second distillation
apparatus of the
thermal separation unit. In a further embodiment, the bottoms mixture (B1)
and/or
optionally the lower phase (L2) is fed into the third phase separation vessel
of the thermal
dissociation unit.
In a further embodiment, the bottoms mixture (61) and/or optionally the lower
phase (L2) is
fed both into the second distillation apparatus of the thermal dissociation
unit, and into the
third phase separation apparatus of the thermal dissociation unit. For this
purpose, the
bottoms mixture (B1) and/or optionally the lower phase (L2) is divided into
two
substreams, in which case one substream is supplied to the second distillation
apparatus
and one substream to the third phase separation apparatus of the thermal
dissociation
unit.
The invention is illustrated by the drawings and examples which follow,
without restricting it
thereto.
The individual drawings show:
figure 1 a block diagram of a preferred embodiment of the process
according to the
invention,
figure 2 a block diagram of a further preferred embodiment of the process
according to
the invention.
In figures 1 and 2, the reference numerals are defined as follows:
Figure 1
1-1 hydrogenation reactor
11-1 first distillation apparatus
111-1 third phase separation apparatus (of the thermal dissociation
unit)
IV-1 second distillation apparatus (of the thermal dissociation unit)
1 stream comprising carbon dioxide
2 stream comprising hydrogen
3 stream comprising formic acid-amine adduct ((A2), residues of
the
catalyst, polar solvent; (lower phase (L1))
5 stream comprising polar solvent; (distillate (D1))
6 stream comprising tertiary amine (Al) (upper phase (U2)) and
formic
acid-amine adduct (A2) (lower phase (L2)); bottoms mixture (B1)
CA 02854047 2014-04-30
7 stream comprising formic acid-amine adduct (A2); lower phase
(L3)
8 stream comprising tertiary amine (Al) (upper phase (U3)) and
formic
acid-amine adduct (A2) (lower phase (L3)); bottoms mixture (B2)
9 stream comprising formic acid; (distillate (D2))
5 10 stream comprising tertiary amine (Al); upper phase (U3)
Figure 2
1-2 hydrogenation reactor
10 11-2 first distillation apparatus
111-2 third phase separation apparatus (of the thermal dissociation
unit)
1V-2 second distillation apparatus (of the thermal dissociation
unit)
V-2 first phase separation apparatus
V1-2 extraction unit
11 stream comprising carbon dioxide
12 stream comprising hydrogen
13a stream comprising hydrogenation mixture (H)
13b stream comprising lower phase (L1)
13c stream comprising raffinate (R2)
15 stream comprising distillate (D1)
16 stream comprising bottoms mixture (B1)
17 stream comprising lower phase (L3)
18 stream comprising bottoms mixture (B2)
19 stream comprising formic acid; (distillate (02))
20 stream comprising upper phase (U3)
21 stream comprising extract (E2)
22 stream comprising upper phase (U1)
In the embodiment according to figure 1, a stream 1 comprising carbon dioxide
and a
stream 2 comprising hydrogen are supplied to a hydrogenation reactor 1-1. It
is possible to
supply further streams (not shown) to the hydrogenation reactor 1-1, in order
to
compensate for any losses of the tertiary amine (Al) or of the catalyst which
occur.
In the hydrogenation reactor 1-1, carbon dioxide and hydrogen are converted in
the
presence of a tertiary amine (Al), of a polar solvent and of a transition
metal complex as
the catalyst. This affords a biphasic hydrogenation mixture (H) which
comprises an upper
phase (U1) comprising the catalyst and the tertiary amine (Al)., and a lower
phase (L1)
comprising the polar solvent, residues of the catalyst and the formic acid-
amine adduct
(A2).
CA 02854047 2014-04-30
36
The lower phase (L1) is supplied as stream 3 to the distillation apparatus 11-
1. The upper
phase (U1) remains in the hydrogenation reactor 1-1. In the embodiment
according to
figure 1, the hydrogenation reactor 1-1 functions simultaneously as the first
phase
separation apparatus.
In the first distillation apparatus 11-1, the lower phase (L1) is separated
into a distillate (D1)
comprising the polar solvent, which is recycled as stream 5 to the
hydrogenation reactor I-
1, and into a biphasic bottoms mixture (B1) comprising an upper phase (U2),
which
comprises the tertiary amine (Al), and the lower phase (L2), which comprises
the formic
acid-amine adduct (A2).
The bottoms mixture (B1) is supplied as stream 6 to the third phase separation
apparatus
111-1 of the thermal dissociation unit.
In the third phase separation apparatus III-1 of the thermal dissociation
unit, the bottoms
mixture (B1) is separated to obtain an upper phase (U3), which comprises the
tertiary
amine (Al), and a lower phase (L3), which comprises the formic acid-amine
adduct (A2).
The upper phase (U3) is recycled as stream 10 to the hydrogenation reactor l-
1. The lower
phase (L3) is supplied as stream 7 to the second distillation apparatus IV-1
of the thermal
dissociation unit. The formic acid-amine adduct (A2) present in the lower
phase (L3) is
separated in the second distillation apparatus IV-1 into formic acid and free
tertiary amine
(Al). In the second distillation apparatus IV-1, a distillate (D2) and a
biphasic bottoms
mixture (B2) are obtained.
The distillate (D2) comprising formic acid is discharged as stream 9 from the
distillation
apparatus IV-1. The biphasic bottoms mixture (62) comprising the upper phase
(U3),
which comprises the tertiary amine (Al), and the lower phase (L3), which
comprises the
formic acid-amine adduct (A2), is recycled as stream 8 to the third phase
separation
apparatus 111-1 of the thermal dissociation unit. In the third phase
separation apparatus III-
1, the bottoms mixture (B2) is separated into upper phase (U3) and lower phase
(L3). The
upper phase (U3) is recycled as stream 10 to the hydrogenation reactor 1-1.
The lower
phase (L3) is recycled as stream 7 to the second distillation apparatus IV-1.
In the embodiment according to figure 2, a stream 11 comprising carbon dioxide
and a
stream 12 comprising hydrogen are supplied to a hydrogenation reactor 1-2. It
is possible
to supply further streams (not shown) to the hydrogenation reactor 1-2, in
order to
compensate for any losses of the tertiary amine (Al) or of the catalyst which
occur.
CA 02854047 2014-04-30
37
In the hydrogenation reactor 1-2, carbon dioxide and hydrogen are converted in
the
presence of a tertiary amine (Al), of a polar solvent and of an iron complex
as the catalyst.
This affords a biphasic hydrogenation mixture (H) which comprises an upper
phase (U1)
comprising the catalyst and the tertiary amine (Al), and a lower phase (L1)
comprising the
polar solvent, residues of the catalyst and the formic acid-amine adduct (A2).
The hydrogenation mixture (H) is supplied as stream 13a to a first phase
separation
apparatus V-2. In the first phase separation apparatus V-2, the hydrogenation
mixture (H)
is separated into the upper phase (U1) and the lower phase (L1).
The upper phase (U1) is recycled as stream 22 to the hydrogenation reactor 1-
2. The lower
phase (L1) is supplied as stream 13b to the extraction unit VI-2. The lower
phase (L1) is
extracted therein with the tertiary amine (Al), which is recycled as stream 20
(upper phase
(U3)) from the third phase separation apparatus 111-2 to the extraction
apparatus VI-2.
In the extraction unit VI-2, a raffinate (R2) and an extract (E2) are
obtained. The raffinate
(R2) comprises the formic acid-amine adduct (A2) and the polar solvent and is
supplied as
stream 13c to the first distillation apparatus 11-2. The extract (E2)
comprises the tertiary
amine (Al) and the residues of the complex catalyst and is recycled as stream
21 to the
hydrogenation reactor 1-2.
In the first distillation apparatus 11-2, the raffinate (R2) is separated into
a distillate (D1)
comprising the polar solvent, which is recycled as stream 15 to the
hydrogenation reactor
1-2, and into a biphasic bottoms mixture (B1).
The bottoms mixture (B1) comprises an upper phase (U2), which comprises the
tertiary
amine (Al), and a lower phase (L2), which comprises the formic acid-amine
adduct (A2).
The bottoms mixture (B1) is supplied as stream 16 to the second distillation
apparatus IV-
2.
The formic acid-amine adduct present in the bottoms mixture (B1) is separated
in the
second distillation apparatus IV-2 into formic acid and free tertiary amine
(Al). In the
second distillation apparatus IV-2, a distillate (D2) and a bottoms mixture
(B2) are
obtained.
The distillate (D2) comprising formic acid is discharged as stream 19 from the
second
distillation apparatus IV-2. The biphasic bottoms mixture (B2) comprising the
upper phase
(U3), which comprises the tertiary amine (Al), and the lower phase (L3), which
comprises
the formic acid-amine adduct (A2), is recycled as stream 18 to the third phase
separation
apparatus 111-2 of the thermal dissociation unit.
CA 02854047 2014-04-30
38
In the third phase separation apparatus 111-2 of the thermal dissociation
unit, the bottoms
mixture (B2) is separated to obtain an upper phase (U3) comprising the
tertiary amine
(Al), and a lower phase (L3) comprising the formic acid-amine adduct (A2).
The upper phase (U3) is recycled from the third phase separation apparatus 111-
2 as
stream 20 to the extraction unit VI-2. The lower phase (L3) is supplied as
stream 17 to the
second distillation apparatus IV-2 of the thermal dissociation unit. The
formic acid-amine
adduct (A2) present in the lower phase (L3) is separated in the second
distillation
apparatus IV-2 into formic acid and free tertiary amine (Al). In the second
distillation
apparatus IV-2, as detailed above, another distillate .(D2) and another
bottoms mixture
(B2) are obtained.
Examples
Synthesis of the chelate phosphine lioands:
Bis(dipentadecylphosphino)ethane: 250 ml of pentadecylmagnesium bromide (15%
in
tetrahydrofuran (THF); 119 mmol) are initially charged in a 1 1 4-neck flask
with internal
thermometer, argon blanketing, metal/water condenser and stirrer, and cooled
to -30 C.
Subsequently, a solution of 5.5 g (23.8 mmol) of 1,2-
bis(dichlorophosphino)ethane in
100 ml of THF is added dropwise within 30 minutes, in the course of which a
large amount
of solids precipitates. The mixture is then warmed to room temperature within
one hour
and subsequently stirred at internal temperature 50 C for a further 2 hours,
which gives
rise to a grayish-white suspension. This is admixed gradually, and while
cooling with ice,
with 95 ml of saturated and degassed NH4CI solution to obtain a white
suspension.
Another 65 ml of degassed water are added thereto and the precipitate is
filtered off with
suction through a G2 frit under argon. The product is washed once with water
and twice
with 20 ml of THF, and dried under reduced pressure. This gives 22.2 g (93.5%)
of the
product in the form of a white powder.
31P NMR (CDCI3): -26.8 ppm (s); elemental analysis: calc. C 79.6%, H 13.8%, P
6.6%;
exp. C 79.5%, H 14.0%, P 6.3%, Br 0.04%, Cl 0.06%, 0 <0.5%.
Bis(dioctadecylphosphino)ethane: 100 ml of octadecylmagnesium bromide (0.5 M
in THF;
50 mmol) are initially charged in a 1 I 4-neck flask with internal
thermometer, argon
blanketing, metal/water condenser and stirrer, and cooled to -30 C.
Subsequently, a
CA 02854047 2014-04-30
39
solution of 2.3 g (10 mmol) of 1,2-bis(dichlorophosphino)ethane in 100 ml of
THF is added
dropwise within 40 minutes, in the course of which a large amount of solids
precipitates.
The mixture is then warmed to room temperature within one hour and
subsequently stirred
at internal temperature 50 C for a further 2 hours, which gives rise to a
grayish-white
suspension. This is admixed gradually, and while cooling with ice, with 50 ml
of saturated
and degassed NH4CI solution to obtain a white suspension. Another 50 ml of
degassed
water are added thereto and the precipitate is filtered off with suction
through a G2 frit
under argon. The product is washed once with water and twice with 10 ml of
THF, and
dried under reduced pressure. This gives 11.0 g (88.0%) of the product in the
form of a
white powder.
31P NMR (CDCI3): -26.1 ppm (s).
The comparative examples (Al-a and Al-b) and the inventive examples (A2-a, A2-
b, A3-a
and A3-b)) demonstrate the hydrogenation of carbon dioxide (CO2) and the reuse
of the
transition metal complex used as the catalyst.
A 100 ml or a 250 ml autoclave made of Hastelloy C (hydrogenation reactor),
equipped
with a paddle stirrer, was charged under inert conditions with the tertiary
amine (Al), the
polar solvent and the catalyst. Subsequently, the autoclave was closed and
carbon dioxide
was injected at room temperature. Thereafter, hydrogen (H2) was injected and
the reactor
was heated while stirring (1000 rpm). After the reaction time, the autoclave
was cooled
and the hydrogenation mixture (H) decompressed, water was added and the
mixture was
stirred at room temperature for 10 minutes.
A biphasic hydrogenation mixture (H) was obtained, and the upper phase (U1)
was
enriched with the free tertiary amine (Al) and the catalyst, and the lower
phase (L1) with
the polar solvent and the formic acid-amine adduct (A2) formed.
The phases were subsequently separated. The formic acid content (in the form
of the
formic acid-amine adduct (A2)) of the lower phase (L1) and the ruthenium
content (CRu) of
both phases were determined by the methods described below. The upper phase
(U1),
comprising ruthenium catalyst, was then supplemented to 85 g with fresh
tertiary amine
(Al) and used again for CO2 hydrogenation with the same solvent, under the
same
reaction conditions as above (see Al -b and A2-b). On completion of reaction
and water
addition, the lower phase (L1) was removed and admixed three times under inert
conditions with the same amount (mass of amine corresponds to the mass of the
lower
phase) of fresh tertiary amine (Al) (stir at room temperature for 10 minutes
and then
separate phases) for catalyst extraction.
CA 02854047 2014-04-30
The total content of formic acid in the formic acid-amine adduct (A2) was
determined
potentiometrically by titration with 0.1 N KOH in Me0H with a "Mettler Toledo
DL50"
titrator. The ruthenium content was determined by AAS. The parameters and
results of the
5 individual experiments are reported in table 1.
The comparative examples (Al-a and Al -b) and the inventive examples (A2-a, A2-
b, A3-a
and A3-b) show that the catalyst can be recycled into the CO2 hydrogenation
and reused
there. The transition metal complexes used in accordance with the invention as
catalysts
10 can be depleted down to less than or equal to 1 ppm by phase separation
alone.
-
Table 1
Comparative example Al-a (first Comparative example Al-b
Inventive example A2-a (first Inventive example A2-b (reuse
hydrogenation) (reuse of the catalyst and
hydrogenation) of the catalyst and extraction)
extraction)
Tertiary amine (Al) 85.0 g trihexylamine upper phase from Al-a 85.0 g
trihexylamine upper phase from A2-a
supplemented to 85 g with
supplemented to 85.0 g with
fresh trihexylamine
fresh trihexylamine
Polar solvent 25.0 g methanol 25.0 g methanol 25.0 g
methanol 25.0 g methanol
(used) 2.0 g water 2.0 g water 2.0 g
water 2.0 g water
(-)
Catalyst 0.34 g pu(Pnocty13)4(H)2], 0.16 g 1,2- upper phase
from A-la 0.34 g [Ru(Pnocty13)4(H)2], 0.16 g 1,2- upper phase from A2-
a
0
bis(didodecylphosphino)ethane
bis(dipentadecylphosphino)ethane iv
co
Injection of CO2 to 2.7 MPa abs to 2.4 MPa abs to 2.8
MPa abs to 3.0 MPa abs ul
,i=
0
Injection of H2 to 12.20MPa abs to 11.9 MPa to 12.0
MPa abs to 11.7 MPa abs ,i=
-.3
Heating 70 C 70 C 70 C
70 C iv
0
Reaction time 1.0 hour 1.0 hour 1.0
hour 1.0 hour H
,i=
Water addition after the 2.2 g 2.1 g 2.2 g
2.1 g -D. o
......
Fi.
reaction
wi
Upper phase (U1) 49.3 g 54.5 g 38.5
g 53.7 g 0
Lower phase (L1) 64.4 g 58.5 g 74.7
g 58.9 g
7.1% formic acid 6.7% formic acid 7.1%
formic acid 6.8% formic acid
cRõ upper phase (U1) 250 ppm 270 ppm 280
ppm 240 ppm
after reaction and water
addition
cRõ lower phase (L1) 4 ppm 5 ppm 1 ppm
1 ppm
after reaction and water
addition
Table 2
Inventive example A3-a (first Inventive example A3-b
(reuse of the catalyst and
hydrogenation)
extraction)
Tertiary amine (Al) 85.0 g trihexylamine 36.7 g upper phase from
A3-a supplemented to 85 g
with fresh trihexylamine
Polar solvent 25.0 g methanol 25.0 g
methanol
(used) 2.0 g water 2.0 g
water
Catalyst 0.32 g [Ru(PnOcty13)4(H)21, 0.22 g 1,2- upper phase
from A-3a 0
bis(dioctadecylphosphino)ethane
co
Injection of CO2 to 2.3 MPa abs to 2.4 MPa
abs 0
Injection of H2 to 11.8 MPa abs to 11.6 MPa
0
Heating 70 C 70 C
Reaction time 1.0 hour 1.0 hour
0
Water addition after 2.2 g 2.1 g
0
the reaction
Upper phase (U1) 41.0 g 37.9g
Lower phase (L1) 75.0 g 76.3 g
8.8% formic acid 7.8% formic
acid
cRi, in upper phase 390 ppm 310 ppm
(U1) after reaction and
addition of water
cRt, in lower phase (L1) 2 ppm 1 ppm
after reaction and
addition of water
