Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS FOR PREPARING METHYL FORMATE BY REACTION OF METHANOL
WITH CARBON MONOXIDE IN THE PRESENCE OF A CATALYST SYSTEM
COMPRISING ALKALI METAL FORMATE AND ALKALI METAL ALKOXIDE
Description
The present invention relates to a process for preparing methyl formate by
reaction of
methanol with carbon monoxide in the presence of a catalyst system comprising
an
alkali metal formate and an alkali metal alkoxide.
Methyl formate (the methyl ester of formic acid) is an important intermediate
for the
preparation of formic acid, where methyl formate is hydrolyzed by means of
water to
form formic acid and methanol. Methyl formate is also used for preparing
acetaldehyde by hydroisomerization over rhodium or iridium catalysts. In
addition, the
isomerization of methyl formate to acetic acid and the oxidative reaction of
methyl
formate with methanol over selenium catalysts to form dimethyl carbonate have
been
described (Hans-JCirgen Arpe, IndustrieIle Organische Chemie, 6th edition,
2007, page
48).
Methyl formate has been produced industrially for over 80 years by
carbonylation of
methanol. The carbonylation is generally carried out in the presence of a base
as
catalyst, in particular using sodium methoxide (sodium methylate) as catalyst.
The
reaction is generally carried out at about 70 C and a pressure of up to 200
bar
(Ullmanns Encyclopedia of Technical Chemistry, 6th edition (2003), volume 15,
pages
5 to 8; Wiley-VCH-Verlag, DOI: 10.1002/14356007.a12_013).
The carbonylation of methanol is a homogeneously catalyzed equilibrium
reaction in
which the equilibrium is shifted in the direction of methyl formate with
increasing
carbon monoxide partial pressure and decreasing temperature. In the continuous
carbonylation of methanol, not only the position of the equilibrium but also a
sufficiently high reaction rate are necessary for an economic process with an
acceptable space-time yield (STY). The reaction rate of the carbonylation of
methanol
can be increased by increasing the temperature or increasing the carbon
monoxide
partial pressure. However, increasing the reaction rate by the above-described
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methods is associated with disadvantages. Thus, increasing the temperature
leads, as
described above, to a deterioration in the position of the equilibrium, which
in turn
leads to a deterioration in the space-time yield. There are now numerous
processes
with various embodiments which are carried out to achieve an acceptable space-
time
yield under high pressure (up to 200 bar). However, these high-pressure
processes
require specially designed reactors which are associated with high capital
costs for the
reactor.
WO 2001/07392 describes a process for the preparation of methyl formate, in
which
the reaction of methanol with carbon monoxide is carried out at a carbon
monoxide
pressure of from 9 to 18 MPa (from 90 to 180 bar) in the presence of from 0.05
to
0.5% by weight of an alkali metal methoxide, based on the weight of the liquid
reactor
feed. In the description of WO 2001/07392, it is indicated that the alkali
metal
methoxide used as catalyst is converted into the catalytically inactive alkali
metal
formate by, in particular, two undesirable but unavoidable secondary
reactions. The
alkali metal formate is also referred to as consumed catalyst or catalyst
degradation
product. The alkali metal formate can be formed here by reaction of alkali
metal
methoxide with methyl formate to give alkali metal formate and dimethyl ether
according to equation (i). In addition, alkali metal formate is formed in the
presence of
traces of water from alkali metal methoxide and methyl formate by hydrolysis
according to equation (ii), forming methanol and alkali metal formate. The
secondary
reactions (i) and (ii) are illustrated below for the example of the formation
of sodium
formate from sodium methoxide.
(i) NaOCH3 + HCOOCH3 HCOONa + CH3OCH3
(ii) NaOCH3 + H20 + HCOOCH3 HCOONa + 2 CH3OH
In the process according to WO 2001/07392, the methyl formate formed is driven
off
from the reactor output in a distillation apparatus. The unconsumed alkali
metal
methoxide used as catalyst can be recirculated to the carbonylation reactor.
However,
it is necessary to remove the catalyst degradation products in a desalting
apparatus
before recirculation in order to prevent precipitation of salts. The alkali
metal formate
occurring as catalyst degradation product can lead to deposits in the
apparatuses and
pipes through to blockage of pipes and valves because of its insufficient
solubility.
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According to the teaching of WO 2001/07392, the content of alkali metal
formate at
the reactor outlet is preferably in the range from 0.1 to 0.3% by weight.
WO 2003/089398 likewise describes a process for preparing methyl formate from
methanol and carbon monoxide in the presence of an alkali metal alkoxide in
concentrations of from 0.01 to 2 mol per kg of liquid reaction mixture. There
too, the
alkali metal formate is described as undesirable catalyst degradation product
which is
discharged to prevent salt-like deposits. In addition, this process requires
recirculation,
which is complicated in terms of apparatus, of a gas stream which has an
average
superficial gas velocity in the range from 1 to 20 m/s.
Ullmanns Encyclopedia of Technical Chemistry (2005, chapter "Formic Acid',
pages 6
to 7; Wiley-VCH-Verlag, DOI: 10.1002/14356007.a12_013) also states that
dimethyl
ether and the catalytically inactive sodium formate are formed from sodium
methoxide
in an undesirable secondary reaction with methyl formate.
PEP-Review (Process Economics Program "Formic Acid', 1983, pages 50 to 52)
describes a process for preparing methyl formate from methanol and carbon
monoxide in the presence of sodium formate. The alkali metal formate formed is
referred to as consumed or inactive catalyst. The catalyst, sodium. methoxide,
can be
recirculated to the reactor. However, for this it is necessary to discharge
the sodium
formate formed from the process in such amounts that the molar ratio of
consumed
catalyst (sodium formate) to catalyst (sodium methoxide) is not more than
equimolar.
US 2004/0171704 describes a process for preparing methanol or formic esters by
reaction of carbon monoxide with an alcohol. As catalysts, preference is given
to using
alkali metal salts. The objective of US 2004/0171704 is to make the reaction
of carbon
monoxide with the alcohol possible even in the presence of water and/or carbon
dioxide. Catalysts described are alkali metal carbonates, alkali metal
nitrates, alkali
metal phosphates, alkali metal acetates and alkali metal formates. The use of
alkali
metal alkoxides is explicitly ruled out since these are deactivated in the
presence of
water and/or carbon dioxide.
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EP 0 596 483 describes a process for preparing methyl formate by carbonylation
of
methanol in the presence of sodium methoxide or potassium methoxide as
catalyst.
EP 0 596 483, too, states that the alkali metal methoxide (alkali metal
methylate) used
as catalyst is converted into inactive decomposition products such as sodium
formate
or potassium formate, sodium carbonate or potassium carbonate and sodium
hydrogencarbonate or potassium hydrogencarbonate. The decomposition products
are removed periodically by means of a filter, with about 0.9% by weight of
decomposition products occurring at the reactor outlet. The decomposition
products
are composed of about 38% by weight of sodium formate, 42% by weight of sodium
hydrogencarbonate, 15% by weight of sodium carbonate and 6% by weight of
sodium
methoxide. To reduce catalyst consumption and increase the space-time yield,
the
reaction is carried out in the presence of a specific sodium or potassium
oxaperfluoroalkanesulfonate and a strong organic base.
Disadvantages of the processes described in the prior art are that very high
pressures
are required in order to achieve acceptable space-time yields and/or
recirculations,
which are complicated in terms of apparatus, of recycle gas streams having
high
superficial gas velocities are necessary. These processes require specially
designed
reactors which are associated with high capital cost. Although relatively low
carbon
monoxide partial pressures of 3.0 MPa (30 bar) are possible in the process
described
in EP 0 596 483, the use of very expensive sodium or potassium
oxaperfluoroalkanesulfonates and strong organic bases is necessary.
It was an object of the present invention to provide a process which gives
methyl
formate in good space-time yields. Furthermore, the process should allow a
simpler
process procedure than the processes described in the prior art, in particular
without
the costly high-pressure reactors described in the prior art and without
expensive
catalyst additives such as potassium oxaperfluoroalkanesulfonates and strong
organic
bases.
This object is achieved by a process for preparing methyl formate by
carbonylation of
methanol by means of carbon monoxide in a carbonylation reactor in the
presence of
a catalyst system comprising alkali metal formate and alkali metal alkoxide to
give a
reaction mixture (Rm) which comprises methyl formate, alkali metal formate,
alkali
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metal alkoxide and possibly unreacted methanol and unreacted carbon monoxide
and
is taken from the carbonylation reactor, wherein the reaction mixture (Rm)
comprises
at least 0.5% by weight of alkali metal alkoxide based on the total weight of
the
reaction mixture (Rm) and the molar ratio of alkali metal formate to alkali
metal
5 alkoxide in the reaction mixture (Rm) is greater than 1.
Very good space-time yields which are sometimes even above the space-time
yields
described in the prior art are achieved in the process of the invention for
preparing
methyl formate from methanol and carbon monoxide. The process of the invention
has
the disadvantage that it makes it possible to obtain methyl formate in good
yields even
at relatively low pressures. This enables costs to be saved in reactor design.
In
addition, the process of the invention gives very good space-time yields
without the
use of expensive additives such as potassium oxaperfluoroalkanesulfonates and
strong organic bases being necessary. The problems of salt deposits, which can
lead
to blockages in pipes and valves, described in the prior art can also be
reduced or
even completely prevented by the process of the invention.
In the prior art, there was the established belief that only alkali metal
alkoxides are
catalytically active in respect of the carbonylation of methanol. On the other
hand,
alkali metal formates are described as catalytically inactive in the prior
art. In the prior
art, alkali metal formates are also described as consumed catalysts which have
to be
removed from the reaction mixture and replaced by fresh, catalytically active
alkali
metal alkoxide.
It has surprisingly been found that alkali metal formate in combination with
alkali metal
alkoxide is catalytically active in respect of the carbonylation of methanol,
contrary to
the established belief in the prior art. This applies in particular to a
mixture comprising
alkali metal formate and alkali metal alkoxide in a molar ratio of alkali
metal formate to
alkali metal alkoxide of greater than 1, preferably greater than 2,
particularly preferably
greater than 3 and in particular greater than 5.
The present invention therefore also provides for the use of a mixture which
comprises an alkali metal formate and an alkali metal alkoxide and in which
the molar
ratio of alkali metal formate to alkali metal alkoxide is greater than 1,
preferably
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greater than 2, particularly preferably greater than 3 and in particular
greater than 5 as
catalyst system for preparing methyl formate by carbonylation of methanol by
means
of carbon monoxide.
Reaction of methanol with carbon monoxide to form methyl formate
The carbon monoxide used in the process of the invention can be used in solid,
liquid
or gaseous form. Carbon monoxide can be used as pure material, i.e. having a
content of at least 95% by weight, preferably at least 97% by weight and
particularly
preferably at least 99% by weight. Carbon monoxide is preferably used in
gaseous
form. The carbon monoxide used is preferably very largely free of carbon
dioxide, i.e.
generally comprises less than 1% by weight of carbon dioxide, preferably less
than
0.5% by weight of carbon dioxide, in each case based on the total weight of
the gas
mixture comprising carbon monoxide. It is also possible to use gas mixtures
which
comprise carbon monoxide and in addition to carbon monoxide comprise further
inerts
such as nitrogen, hydrogen, methane or noble gases. However, the content of
inerts is
generally below 10% by weight, based on the total weight of the gas mixture
comprising carbon monoxide. Although larger amounts may likewise be tolerable,
they
generally require the use of relatively high pressures, as a result of which
additional
compression energy is required. The carbon monoxide generally comes from the
carbon monoxide sources with which a person skilled in the art will be
familiar, for
example synthesis gas.
The methanol used in the process of the invention is, in a preferred
embodiment,
essentially water-free, i.e. the methanol used comprises not more than 250 ppm
by
weight, preferably not more than 100 ppm by weight and particularly preferably
not
more than 50 ppm by weight, of water, in each case based on the total weight
of
methanol used and the water comprised therein.
In a preferred embodiment, the carbonylation of methanol by means of carbon
monoxide is carried out in the absence of water. For the purposes of the
present
invention, in the absence of water means that the reaction mixture (Rm)
comprises not
more than 250 ppm by weight, preferably not more than 100 ppm by weight and
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particularly preferably not more than 50 ppm by weight, of water, in each case
based
on the total weight of the reaction mixture (Rm).
The alkali metal alkoxide used in the process of the invention can be used as
solid or
as a solution in a suitable solvent. It is possible to use mixtures of two or
more alkali
metal alkoxides. For the purposes of the present invention, the term alkali
metal
alkoxide encompasses both one alkali metal alkoxide and also mixtures of two
or
more alkali metal alkoxides. However, preference is given to using only one
alkali
metal alkoxide. In a preferred embodiment, an alkali metal methoxide dissolved
in
methanol is used.
The alkali metal formate used in the process of the invention can likewise be
used as
solid or as a solution in a suitable solvent. It is possible to use mixtures
of two or more
alkali metal formates. For the purposes of the present invention, the term
alkali metal
formate encompasses both one alkali metal formate and also mixtures of two or
more
alkali metal formates. However, preference is given to using only one alkali
metal
formate. In a preferred embodiment, an alkali metal formate dissolved in
methanol is
used. The alkali metal formate can also be fed to the carbonylation reactor by
recirculation from downstream work-up stages.
The alkali metal components of the alkali metal formate and of the alkali
metal
alkoxide can be selected independently from the group consisting of lithium,
sodium,
potassium, rubidium and cesium. The alkali metal formate can therefore be
selected
from the group consisting of lithium formate, sodium formate, potassium
formate,
rubidium formate and cesium formate. The alkali metal formate is preferably
selected
from the group consisting of sodium formate and potassium formate. Particular
preference is given to potassium formate. The alkali metal alkoxide can be
selected
from the group consisting of lithium alkoxide, sodium alkoxide, potassium
alkoxide,
rubidium alkoxide and cesium alkoxide. The alkali metal alkoxide is preferably
selected from the group consisting of sodium alkoxide and potassium alkoxide.
Particular preference is given to potassium alkoxide.
Suitable alkoxide components of the alkali metal alkoxide are alkoxide anions
having
from 1 to 12 carbon atoms, for example methoxide, ethoxide, 1-propoxide, 2-
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propoxide, 1-butoxide, 2-butoxide, 2-methyl-1-propoxide, 2-methyl-2-propoxide,
1-
pentoxide, isopentoxide, 1-hexoxide, 1-heptoxide, 1-octoxide, 2-ethyl-1-
hexoxide, 1-
nonoxide, 3,5,5-trimethy1-1-hexoxide, 2,6-dimethy1-4-heptoxide and 1-decoxide.
Particular preference is given to methoxide as alkoxide.
The alkali metal components of the alkali metal formate and of the alkali
metal
alkoxide are particularly preferably identical.
In particular, the alkali metal formate is potassium formate and the alkali
metal
alkoxide is potassium methoxide.
In the process of the invention, a mixture of alkali metal formate and alkali
metal
alkoxide, where the molar ratio of alkali metal formate to alkali metal
alkoxide in the
mixture is greater than 1, is preferably used as catalyst system. The molar
ratio of
alkali metal formate to alkali metal alkoxide is preferably in the range from
2 to 20,
particularly preferably in the range from 2 to 15, very particularly
preferably in the
range from 3 to 10 and in particular in the range from 3 to 8, with potassium
formate
being particularly preferred as alkali metal formate and potassium methoxide
being
particularly preferred as alkali metal alkoxide.
The molar ratio of alkali metal formate to alkali metal alkoxide in the
reaction mixture
(Rm) is preferably greater than 2, particularly preferably greater than 3 and
in particular
greater than 5.
The molar ratio of alkali metal formate to alkali metal alkoxide in the
reaction mixture
(Rm) is preferably in the range from 2 to 20, particularly preferably in the
range from 2
to 15, very particularly preferably in the range from 3 to 10 and in
particular in the
range from 3 to 8, with potassium formate being particularly preferred as
alkali metal
formate and potassium methoxide being particularly preferred as alkali metal
alkoxide.
In a preferred embodiment, a catalyst system consisting essentially of the
above-
described mixture of alkali metal formate and alkali metal alkoxide is used in
the
process of the invention, with a mixture consisting essentially of potassium
formate
and potassium methoxide being particularly preferred.
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This means that generally not more than 1% by weight, preferably not more than
0.5%
by weight and particularly preferably not more than 0.1% by weight and in
particular
none of further catalytically active substances which catalyze the
carbonylation of
methanol by means of carbon monoxide are used in addition to the mixture of
alkali
metal formate and alkali metal alkoxide used as catalyst system in the process
of the
invention, in each case based on the total weight of the mixture used as
catalyst
system and any further catalytically active substances present. In a preferred
embodiment, the mixture used as catalyst system consists of alkali metal
formate and
alkali metal alkoxide, with a mixture consisting of potassium formate and
potassium
methoxide being particularly preferred.
In a preferred embodiment of the process of the invention, no alkali metal
oxaperfluorosulfonates and also no strong organic bases having a pKa of
greater than
8.7 are present. Examples of alkali metal oxaperfluorosulfonates which are not
present in the process of the invention are those of the general formula
CF3CF2(0CFXCF2)p OCF2S03M
where p = 0 to 2, X = F, CF3 and M = Na, K.
The present invention therefore also provides for the use of a mixture of an
alkali
metal formate and an alkali metal alkoxide as catalyst system for the reaction
of
methanol with carbon monoxide to form methyl formate, wherein the molar ratio
of
alkali metal formate to alkali metal alkoxide in the mixture is greater than
1. The
abovementioned preferences in respect of the alkali metal formate and the
alkali metal
alkoxide and also the molar ratios apply analogously to the use according to
the
invention of the mixture.
As carbonylation reactors in the process of the invention, it is in principle
possible to
use all reactors which are suitable for gas/liquid reactions. Suitable
standard reactors
for gas-liquid reaction systems are indicated, 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".
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Examples which may be mentioned are stirred tank reactors, tube reactors, jet
loop
reactors or bubble columns.
The carbonylation of methanol by means of carbon monoxide can be carried out
5 continuously or batchwise in the process of the invention. In the
batchwise mode of
operation, the carbonylation reactor is charged with the desired liquid and
optionally
solid starting materials and auxiliaries and is subsequently pressurized with
carbon
monoxide to the desired pressure at the desired temperature. After the
reaction is
complete, the carbonylation reactor is normally depressurized. In the
continuous mode
10 of operation, methanol, carbon monoxide, the catalyst system (alkali
metal formate
and alkali metal alkoxide, preferably alkali metal methoxide and alkali metal
formate)
are fed continuously into the carbonylation reactor. Accordingly, the reaction
mixture
(Rm) is discharged continuously from the carbonylation reactor so that the
liquid level
in the carbonylation reactor remains the same on average. The continuous
carbonylation of methanol by means of carbon monoxide is preferred.
A liquid phase and a gas phase are generally present in the carbonylation
reactor.
The carbonylation reaction generally takes place in the liquid phase.
According to the present invention, the reaction mixture (Rm) is the fraction
which is
liquid under the reaction conditions of the carbonylation and is taken off
from the
carbonylation reactor.
The reaction mixture (Rm) thus describes the composition of the liquid phase
which is
taken off from the carbonylation reactor under the reaction pressure of the
carbonylation, i.e. before depressurization.
The carbonylation reaction of methanol with carbon monoxide generally takes
place in
the liquid phase at a total pressure in the range from 30 to 100 bar,
preferably in the
range from 30 to 70 bar and particularly preferably in the range from 50 to 65
bar, and
at a temperature in the range from 60 to 140 C, preferably in the range from
65 to
110 C and particularly preferably in the range from 70 to 100 C, in the
carbonylation
reactor. In a very particularly preferred embodiment, the carbonylation in the
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carbonylation reactor is carried out at a temperature in the range from 70 to
100 C
and a total pressure in the range from 50 to 65 bar.
The molar feed ratio of the amount of methanol fed into the carbonylation
reactor to
the amount of carbon monoxide fed into the carbonylation reactor is generally
from 1
to 5, preferably from 2 to 5, particularly preferably from 2.5 to 4 and in
particular from
3 to 4, in the process of the invention. The amount of methanol fed into the
carbonylation reactor is made up of the freshly introduced methanol and any
methanol
recirculated from downstream work-up stages. The amount of carbon monoxide fed
into the carbonylation reactor is made up of the freshly introduced carbon
monoxide
and any carbon monoxide recirculated from downstream work-up stages.
The molar feed ratio of the amount of methanol fed into the carbonylation
reactor to
the amount of alkali metal alkoxide, preferably potassium methoxide, fed into
the
carbonylation reactor is generally from 100 to 400, preferably from 150 to
350,
particularly preferably from 200 to 350 and in particular from 230 to 330, in
the
process of the invention. The amount of alkali metal alkoxide fed into the
carbonylation reactor is made up of the freshly introduced alkali metal
alkoxide and
any alkali metal alkoxide recirculated from downstream work-up stages.
The molar feed ratio of the amount of methanol fed into the carbonylation
reactor to
the amount of alkali metal formate, preferably potassium formate, fed into the
carbonylation reactor is generally from 25 to 400, preferably from 30 to 200,
particularly preferably from 30 to 100 and in particular from 30 to 50, in the
process of
the invention. The amount of alkali metal formate fed into the carbonylation
reactor is
made up of the freshly introduced alkali metal formate and any alkali metal
formate
recirculated from downstream work-up stages.
For the purposes of the present invention, "freshly introduced" in respect of
methanol,
carbon monoxide, alkali metal alkoxide and alkali metal formate refers to the
components which are not recirculated from downstream work-up stages. These
are
components which do not originate from the process of the invention but are
instead
introduced from outside into the process of the invention.
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However, the addition of freshly introduced alkali metal formate is not
absolutely
necessary. Alkali metal formate is formed according to the above-described
secondary reactions (i) and/or (ii) during the carbonylation of methanol. In a
preferred
embodiment of the process of the invention, no fresh alkali metal formate is
introduced
into the carbonylation reactor and the alkali metal formate originates
exclusively from
the alkali metal formate recirculated from a downstream work-up stage. In this
embodiment, the alkali metal formate accumulates in the process of the
invention until
the concentration according to the invention of alkali metal formate is
reached in the
reaction mixture (Rm).
Alkali metal alkoxide and alkali metal formate are preferably introduced as a
solution
in methanol into the reactor.
In the process of the invention, a reaction mixture (Rm) comprising methyl
formate,
alkali metal formate, alkali metal alkoxide and also any unreacted methanol
and
unreacted carbon monoxide is taken off from the carbonylation reactor. The
composition of the reaction mixture (Rm) in respect of the alkali metal
formate and
alkali metal alkoxide comprised therein depends on the catalyst system used.
The
information and preferences indicated above for the catalyst system apply
analogously to the composition of the reaction mixture (Rm) in respect of the
alkali
metal formate and alkali metal alkoxide comprised therein.
In a preferred embodiment, a mixture which consists essentially of potassium
formate
and potassium methoxide is used as catalyst system, giving a reaction mixture
(Rm)
consisting essentially of methyl formate, potassium formate and potassium
methoxide
and also any unreacted methanol and any unreacted carbon monoxide. For the
purposes of the present invention, "consists essentially of" in respect of the
reaction
mixture (Rm) means that the reaction mixture (Rm) comprises not more than 1%
by
weight, preferably not more than 0.5% by weight, of further components in
addition to
methyl formate, alkali metal formate, alkali metal methoxide and any unreacted
methanol and unreacted carbon monoxide, in each case based on the total weight
of
the reaction mixture (Rm).
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In general, the molar ratio of alkali metal formate to alkali metal alkoxide
in the
reaction mixture (Rm) which is taken off from the carbonylation reactor is
greater than
1. The molar ratio of alkali metal formate to alkali metal alkoxide in the
reaction
mixture (Rm) is preferably in the range from 2 to 20, particularly preferably
in the range
from 2 to 15, very particularly preferably in the range from 4 to 12 and in
particular in
the range from 5 to 10, with potassium formate being particularly preferred as
alkali
metal formate and potassium methoxide being particularly preferred as alkali
metal
alkoxide.
The concentration of the alkali metal alkoxide, preferably the potassium
methoxide, in
the reaction mixture (Rm) is generally at least 0.5% by weight based on the
total
weight of the reaction mixture (Rm). The concentration of the alkali metal
alkoxide in
the reaction mixture (Rm) is preferably in the range from 0.5 to 1.5% by
weight, more
preferably in the range from 0.5 to 1.0% by weight and particularly preferably
in the
range from 0.55 to 0.9% by weight, in each case based on the total weight of
the
reaction mixture (Rm).
The concentration of the alkali metal alkoxide, preferably the potassium
methoxide, in
the reaction mixture (Rm) is generally at least 0.5% by weight based on the
total
weight of the reaction mixture (Rm). The concentration of the alkali metal
alkoxide in
the reaction mixture (Rm) is preferably > 0.5% by weight, particularly
preferably at
least 0.51% by weight, based on the total weight of the reaction mixture (Rm).
The
concentration of the alkali metal alkoxide in the reaction mixture (Rm) is
preferably in
the range from > 0.5 to 1.5% by weight, more preferably in the range from >
0.5 to
1.0% by weight and particularly preferably in the range from 0.51 to 0.9% by
weight, in
particular in the range from 0.55 to 0.9% by weight, in each case based on the
total
weight of the reaction mixture (Rm).
The concentration of the alkali metal formate, preferably the potassium
formate, in the
reaction mixture (Rm) is generally at least 2.25% by weight based on the total
weight
of the reaction mixture (Rm). The concentration of the alkali metal formate is
preferably
in the range from 2.5 to 15% by weight, preferably in the range from 3 to 10%
by
weight and particularly preferably in the range from 5 to 7.5% by weight, in
each case
based on the total weight of the reaction mixture (Rm).
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The percent by weight indicated above for the concentrations of the alkali
metal
formate and of the alkali metal methoxide in the reaction mixture (Rm) are
subject to
the condition that the molar ratio of alkali metal formate to alkali metal
alkoxide in the
reaction mixture (Rm) is greater than 1.
In a particularly preferred embodiment, a reaction mixture (Rm), where the
reaction
mixture (Rm) comprises from 0.5 to 1.5% by weight of alkali metal alkoxide and
from
2.5 to 15% by weight of alkali metal formate, in each case based on the total
weight of
the reaction mixture (Rm), is obtained in the process of the invention.
In a particularly preferred embodiment, a reaction mixture (Rm), where the
reaction
mixture (Rm) comprises from 0.51 to 1.5% by weight of alkali metal alkoxide
and from
2.5 to 15% by weight of alkali metal formate, in each case based on the total
weight of
the reaction mixture (Rm), is obtained in the process of the invention.
The reaction mixture (Rm) generally comprises not more than 48% by weight of
methyl
formate, based on the total weight of the reaction mixture (Rm). The reaction
mixture
(Rm) preferably comprises from 12 to 45% by weight of methyl formate, more
preferably from 25 to 45% by weight and in particular from 35 to 45% by
weight, in
each case based on the total weight of the reaction mixture (Rm).
The reaction mixture (Rm) generally comprises unreacted methanol. The reaction
mixture (Rm) preferably comprises from 40 to 85% by weight of methanol, more
preferably from 45 to 60% by weight and in particular from 45 to 55% by
weight, in
each case based on the total weight of the reaction mixture (Rm).
In a preferred embodiment of the process of the invention, the reaction
mixture (Rm)
comprises
from 12 to 45% by weight of methyl formate,
from 40 to 85% by weight of methanol,
from 2.5 to 15% by weight of alkali metal formate,
from 0.5 to 1.5% by weight of alkali metal alkoxide and
CA 02891452 2015-05-13
from 0 to 2% by weight of carbon monoxide,
where the sum of all components comprised in the reaction mixture (Rm) is 100%
by
weight and the reaction mixture (Rm) comprises not more than 1% by weight,
5 preferably not more than 0.5% by weight, of further components other than
methyl
formate, methanol, alkali metal formate, alkali metal alkoxide, carbon
monoxide and
water, in each case based on the total weight of the reaction mixture (Rm).
In a particularly preferred embodiment of the process of the invention, the
reaction
10 mixture (Rm) comprises
from 35 to 45% by weight of methyl formate,
from 45 to 62% by weight of methanol,
from 2.5 to 7.5% by weight of potassium formate,
15 from 0.5 to 0.8% by weight of potassium methoxide and
from 0 to 1.5% by weight of carbon monoxide,
where the sum of all components comprised in the reaction mixture (Rm) is 100%
by
weight and the reaction mixture (Rm) comprises not more than 1% by weight,
preferably not more than 0.5% by weight, of further components other than
methyl
formate, methanol, potassium formate, potassium methoxide, carbon monoxide and
water, in each case based on the total weight of the reaction mixture (Rm).
Further components which can be comprised in the above amounts in the reaction
mixture (Rm) are, for example, impurities in the starting materials, e.g.
nitrogen, argon,
hydrogen or methane from the carbon monoxide used and impurities such as
formaldehyde and formaldehyde dimethyl acetal from the methanol used and also
impurities comprised in the alkoxides and formates used and by-products from
the
carbonylation of methanol, e.g. dimethyl ether and methyl glyoxal methyl
hemiacetal.
In a preferred embodiment, the liquid feed fed into the carbonylation reactor
is
composed essentially of methanol, alkali metal alkoxide and alkali metal
formate and
optionally methyl formate. In a preferred embodiment, the liquid feed
comprises not
more than 1% by weight, preferably not more than 0.5% by weight, of components
CA 02891452 2015-05-13
16
other than methanol, alkali metal methoxide and alkali metal formate and
optionally
methyl formate, in each case based on the total weight of the liquid feed.
For the present purposes, the term liquid feed encompasses all liquid
components fed
into the reactor, i.e. the sum of freshly introduced and recirculated liquid
components.
The composition of the reaction mixture (Rm) can be controlled via the above-
described feed ratios of carbon monoxide, methanol and catalyst system (alkali
metal
formate and alkali metal alkoxide).
The amount of methyl formate comprised in the reaction mixture (Rm) is made up
of
the amount of methyl formate which is formed from carbon monoxide and methanol
in
the carbonylation reactor and the amount of methyl formate which is optionally
recirculated from a downstream work-up step to the carbonylation reactor.
The amount of carbon monoxide and methanol comprised in the reaction mixture
(Rm)
is controlled via the feed ratios of carbon monoxide to methanol and via the
reaction of
carbon monoxide with methanol to form methyl formate in the carbonylation
reactor
and also via the reaction pressure of the carbonylation.
The setting of the composition of the reaction mixture (Rm) can be carried out
by
conventional methods of regulation known to those skilled in the art, for
example by
means of a measuring unit which measures the composition of the reaction
mixture
(Rm) taken off from the carbonylation reactor and in the event of a deviation
from the
intended composition modifies the feed ratios accordingly.
The amounts of alkali metal formate and alkali metal alkoxide comprised in the
reaction mixture (Rm) are controlled via the amounts of alkali metal formate
and alkali
metal alkoxide fed into the carbonylation reactor, i.e. via the amount and
composition
of the catalyst system. Alkali metal formate and alkali metal alkoxide are
generally
introduced as a solution, preferably a solution in methanol, into the
carbonylation
reactor.
CA 02891452 2015-05-13
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The catalyst system comprising alkali metal formate and alkali metal alkoxide
can be
introduced in fresh form from the outside into the carbonylation reactor. In a
preferred
embodiment, the process of the invention is carried out continuously and the
alkali
metal formate and alkali metal alkoxide comprised in the catalyst system is
recirculated to the carbonylation reactor from a downstream work-up step.
Here, it should be taken into account that the alkali metal alkoxide comprised
in the
catalyst system is partly converted into alkali metal formate in the
carbonylation
reactor. This occurs by reaction of alkali metal alkoxide with methyl formate
to form
alkali metal formate and dimethyl ether and by hydrolysis of alkali metal
alkoxide and
methyl formate by means of traces of water to form alkali metal formate and
methanol.
The formation of alkali metal formate is described with the aid of the
following reaction
equations iii) to v) for the example of the formation of potassium formate
from
potassium methoxide
iii) HCOOCH3 + KOCH3 HCOOK
CH3OCH3
iv) KOCH3 H20 ¨> KOH
CH3OH
v) KOH HCOOCH3 -->
HCOOK CH3OH
To set the composition according to the invention of alkali metal formate and
alkali
metal alkoxide in the reaction mixture (Rm), it is therefore generally
necessary to
separate off part of the alkali metal formate formed according to the reaction
equations iii) to v) from the reaction mixture (Rm). In addition, it is
generally necessary
to replace the alkali metal methoxide which has reacted according to the
reaction
equations iii) and iv).
The removal of the alkali metal formate formed and the replacement of the
alkali metal
alkoxide which has reacted can be carried out sequentially or continuously.
Preference is given to the alkali metal formate formed being continuously
separated
off and the alkali metal alkoxide which has reacted being continuously
replaced by
alkali metal alkoxide freshly introduced from the outside.
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In a particularly preferred embodiment, the reaction mixture (Rm) taken off
from the
carbonylation reactor is subjected to a further work-up comprising the
following steps:
(a) separation of carbon monoxide from the reaction mixture (RM) in a
separation apparatus to give a gas stream (G1) comprising carbon
monoxide and a liquid stream (L1) comprising methyl formate, alkali
metal formate, alkali metal alkoxide and methanol,
(b) separation of the methyl formate from the liquid stream (L1) in a first
distillation apparatus to give a distillate (D1) comprising methyl formate
and a bottom mixture (S1) comprising alkali metal formate, alkali metal
alkoxide and methanol,
(c) division of the bottom mixture (S1) into a substream (S1a) which is
recirculated to the carbonylation reactor and a substream (S1 b) and
(d) separation of the methanol from the substream (S1b) in a second
distillation apparatus to give a distillate (D2) which comprises methanol
and is recirculated to the first distillation apparatus and a bottom
mixture (S2) comprising alkali metal formate and alkali metal alkoxide.
The removal of the carbon monoxide in step (a) is not absolutely necessary. It
is also
possible to feed the reaction mixture (Rm) directly to the first distillation
apparatus in
step (b). If the carbon monoxide is separated off from the reaction mixture
(Rm), the
gas stream (G1) is preferably recirculated to the carbonylation reactor. The
removal of
the carbon monoxide in step (a) is preferably carried out using a flash
apparatus as
separation apparatus.
In step (b), the methyl formate can be separated off completely or partly from
the
liquid stream (L1) or from the reaction mixture (Rm).
In the case of partial removal, for example from 50 to 90% by weight of the
methyl
formate comprised in the liquid stream (L1) or of the methyl formate comprised
in the
reaction mixture (Rm), preferably from 60 to 90% by weight and more preferably
from
CA 02891452 2015-05-13
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80 to 90% by weight, are separated off, in each case based on the total weight
of the
methyl formate comprised in the liquid stream (L1) or of the methyl formate
comprised
in the reaction mixture (Rm).
In a further embodiment of the process of the invention, the methyl formate is
completely separated Off in the first distillation apparatus in process step
(b). For the
purposes of the present invention, "completely separated off' means removal of
more
than 90% of the methyl formate comprised in the liquid stream (L1) or of the
methyl
formate comprised in the reaction mixture (Rm), preferably more than 98.5%,
particularly preferably more than 99%, in particular more than 99.5%, in each
case
based on the total amount of the methyl formate comprised in the liquid stream
(L1) or
of the methyl formate comprised in the reaction mixture (Rm).
In the partial removal of the methyl formate, the bottom mixture (S1) still
comprises
methyl formate. In the case of the complete removal of the methyl formate, the
bottom
mixture (S1) is very largely free of methyl formate. The complete removal of
the
methyl formate is preferred.
The removal of the methyl formate can, for example, be carried out in an
evaporator
or in a distillation unit comprising vaporizer and column, with the column
being filled
with ordered packing, random packing elements and/or plates.
The distillate (D1) separated off in step (b) can still comprise methanol in
addition to
methyl formate. In a preferred embodiment, the distillate (D1) comprises from
60 to
97% by weight of methyl formate and from 3 to 40% by weight of methanol,
preferably
from 75 to 85% by weight of methyl formate and from 15 to 25% by weight of
methanol. The distillate (D1) can be worked up further, for example by
distillation. The
methanol separated off can be recirculated to the carbonylation reactor. The
recirculated methanol can comprise methyl formate.
It is also possible for the methyl formate to be reacted further. The methyl
formate
can, for example, be hydrolyzed to formic acid. The methanol formed here can
likewise be recirculated to the carbonylation reactor. The recirculated
methanol can
comprise methyl formate.
CA 02891452 2015-05-13
The removal of the methyl formate in step (b) gives a bottom mixture (S1)
comprising
alkali metal formate, alkali metal alkoxide and methanol. Alkali metal formate
and
alkali metal alkoxide are preferably present as a solution in methanol in the
bottom
5 mixture (S1).
The control of the amounts of alkali metal formate and alkali metal alkoxide
comprised
in the reaction mixture (Rm) is, in a preferred embodiment, effected by
dividing the
bottom mixture (S1) into the substreams (S1a) and (S1 b).
The separation of the alkali metal formate formed from the reaction mixture
(Rm) is
effected via the substream (S1b). The amount of substream (S1b) separated off
controls the accumulation of the alkali metal formate in the reaction mixture
(Rm). To
discharge the alkali metal formate formed, the substream (S1 b) is fed to the
second
distillation apparatus. To set the composition according to the invention of
the reaction
mixture (Rm), the bottom mixture (S1) is divided in such a way that the weight
ratio of
the substream (S1a) to the substream (S1 b) is greater than 50: 1, preferably
greater
than 100: 1.
In other words, this means that at least 50 parts by weight of substream
(S1a),
preferably at least 100 parts by weight of substream (S1a), per part by weight
of
substream (S1 b) discharged are recirculated to the carbonylation reactor.
At the bottom of the second distillation apparatus, a bottom mixture (52)
comprising
alkali metal formate and alkali metal methoxide is obtained. To prevent
precipitation of
solids and to minimize the risk of encrustations or blockages in the bottom of
the
second distillation apparatus, water is preferably introduced into the second
distillation
apparatus in a preferred embodiment. The water can, for example, be fed as
steam or
steam condensate into the second distillation apparatus.
In this embodiment, the work-up of the reaction mixture (Rm) comprises the
following
steps:
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(a) separation of carbon monoxide from the reaction mixture (Rm) in a
separation apparatus to give a gas stream (G1) comprising carbon
monoxide and a liquid stream (L1) comprising methyl formate, alkali
metal formate, alkali metal alkoxide and methanol,
(b) separation of the methyl formate from the liquid stream (L1) in a first
distillation apparatus to give a distillate (D1) comprising methyl formate
and a bottom mixture (S1) comprising alkali metal formate, alkali metal
alkoxide and methanol,
(c) division of the bottom mixture (S1) into a substream (S1a) which is
recirculated to the carbonylation reactor and a substream (S1b) and
(d) separation of the methanol from the substream (S1b) in a second
distillation apparatus into which water is introduced to give a distillate
(D2) which comprises methanol and is recirculated to the first distillation
apparatus and a bottom mixture (S2w) comprising alkali metal
hydroxide, metal formate and water.
The water can, for example, be fed as steam or steam condensate into the
second
distillation apparatus. The water is, in a preferred embodiment, introduced
into the
bottom of the second distillation apparatus.
The addition of water leads to the alkali metal alkoxide being hydrolyzed to
the
corresponding alkali metal hydroxide and the corresponding alcohol. In the
case of the
preferred potassium methoxide, this is hydrolyzed to potassium hydroxide and
methanol. The methanol formed in this way is likewise separated off as
distillate (D2)
at the top of the second distillation apparatus and is preferably recirculated
to the first
distillation apparatus.
Since not only alkali metal formate but also alkali metal alkoxide are
separated off via
the substream (S1 b), fresh alkali metal alkoxide has to be introduced from
the outside
into the carbonylation reactor. The introduction of the alkali metal alkoxide
from the
outside into the carbonylation reactor is carried out continuously in a
preferred
CA 02891452 2015-05-13
22
embodiment. The freshly introduced alkali metal alkoxide can be introduced as
solid
but is preferably introduced as a solution in methanol into the carbonylation
reactor.
The freshly introduced alkali metal alkoxide can be fed as a separate stream
into the
carbonylation reactor. It is also possible to mix the freshly introduced
alkali metal
alkoxide into the substream (S1a) recirculated from step (c) to the
carbonylation
reactor.
The present invention is illustrated by the following figures and the
following examples
without being restricted thereto.
Figure 1 shows a block diagram of a preferred embodiment of the process of the
invention. In figure 1, the reference numerals have the following meanings:
1 stream comprising carbon monoxide
2 stream comprising methanol
2a stream which comprises methanol and is recirculated from a
downstream
work-up stage
3 stream comprising alkali metal alkoxide dissolved in methanol
4 stream comprising methyl formate, alkali metal formate, alkali metal
alkoxide
and possibly unreacted methanol and unreacted carbon monoxide;
corresponds to reaction mixture (Rm)
5 stream comprising carbon monoxide; corresponds to gas stream (G1)
6 stream comprising methyl formate, alkali metal formate, alkali metal
alkoxide
and methanol; corresponds to liquid stream (L1)
7 stream comprising methyl formate and possibly methanol; corresponds to
distillate (D1)
8 stream comprising alkali metal formate, alkali metal alkoxide and
methanol;
corresponds to bottom mixture (S1)
8a stream comprising alkali metal formate, alkali metal alkoxide and
methanol;
corresponds to substream (S1a)
8b stream comprising alkali metal formate, alkali metal alkoxide and
methanol;
corresponds to substream (S1 b)
9 stream comprising alkali metal formate, alkali metal hydroxide and
water;
corresponds to bottom mixture (S2w)
CA 02891452 2015-05-13
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stream comprising methanol; corresponds to distillate (D2)
1 1 stream comprising water
carbonylation reactor
5 II separation apparatus
111 first distillation apparatus
IV second distillation apparatus
Carbon monoxide, methanol and the catalyst system comprising alkali metal
formate
10 and alkali metal alkoxide are fed into the carbonylation reactor I. In
the carbonylation
reactor, methanol is reacted with carbon monoxide to form methyl formate,
giving the
reaction mixture (Rm). The carbon monoxide is fed in via stream 1 (carbon
monoxide
freshly introduced from the outside) and stream 5 (carbon monoxide
recirculated from
the separation apparatus II). The alkali metal formate and the alkali metal
alkoxide are
recirculated as stream 8a (corresponds to substream S1 a) from the bottom of
the first
distillation apparatus III to the carbonylation reactor. The stream 8a
comprises
methanol, the alkali metal formate and the alkali metal alkoxide, preferably
in
dissolved form.
Losses of alkali metal alkoxide can if necessary be compensated via stream 3.
Stream
3 preferably comprises alkali metal alkoxide dissolved in methanol. Methanol
is
preferably fed into the carbonylation reactor via the streams 2 and/or 2a.
Stream 2
describes the case of fresh methanol being introduced from the outside.
However, it is
also possible, as an alternative or in addition, to introduce the methanol via
stream 2a
which originates from later work-up stages or the reactions of the methyl
formate.
A reaction mixture (Rm) is obtained in the carbonylation reactor I and is
taken off from
the carbonylation reactor I and conveyed as stream 4 to the separation
apparatus II.
In the separation apparatus II, unreacted carbon monoxide is separated off
from the
reaction mixture (Rm). This is preferably carried out by depressurization of
the reaction
mixture (Rm). A gas stream (G1) which consists essentially of carbon monoxide
is
obtained in the separation apparatus II and is recirculated as stream 5 to the
carbonylation reactor I.
CA 02891452 2015-05-13
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A liquid stream (L1) comprising methyl formate, alkali metal formate, alkali
metal
alkoxide and methanol is taken off from the separation apparatus II and is
conveyed
as stream 6 to the first distillation apparatus III. In the first distillation
apparatus III, a
stream 7 comprising methyl formate is separated off at the top of this
distillation
apparatus (distillate (D1)). It is also possible to separate off a mixture of
methyl
formate and methanol at the top of the first distillation apparatus III. In a
preferred
embodiment, the stream 7 is reacted further. Preference is given to
hydrolyzing the
methyl formate to formic acid. The methanol formed in the hydrolysis can be
recirculated as stream 2a to the carbonylation reactor I. At the bottom of the
first
distillation apparatus III, a bottom mixture (S1) comprising alkali metal
formate, alkali
metal alkoxide and methanol is obtained. The bottom mixture (S1) is taken off
as
stream 8 from the distillation apparatus III. The stream 8 is divided into a
substream
8a and a substream 8b. The substream 8a (corresponds to substream S1 a) is
recirculated to the carbonylation reactor I. The stream 8b (corresponds to
substream
S1 b) is worked up further in the second distillation apparatus IV. Water is
fed as
stream 1 1 into the second distillation apparatus IV. Stream 1 1 is preferably
fed into
the bottom of the second distillation apparatus IV. In the second distillation
apparatus
IV, the alkali metal alkoxide comprised in stream 8b is hydrolyzed to the
corresponding alkali metal hydroxide and the corresponding alcohol. In the
case of the
potassium methoxide which is preferably comprised in stream 8b, potassium
hydroxide and methanol are formed in the hydrolysis. Methanol is taken off as
stream
10 at the top of the second distillation apparatus IV and is recirculated to
the first
distillation apparatus III. An aqueous solution comprising potassium
hydroxide,
potassium formate and water is taken off as stream 9 from the second
distillation
apparatus IV.
Figure 2 shows a laboratory apparatus in which the process of the invention is
carried
out. In figure 2, the reference symbols have the following meanings:
A reservoir comprising a mixture of methanol, potassium methoxide and
optionally an alkali metal formate
carbonylation reactor
On-line ATR-FIR measurement sensor (ATR-MIR, Matrix MF from Bruker)
CA 02891452 2015-05-13
10 stream comprising methanol, potassium methoxide and optionally an
alkali
metal formate
11 stream comprising carbon monoxide
12 stream comprising methyl formate, possibly alkali metal formate,
potassium
5 methoxide, methanol and possibly unreacted carbon monoxide
13 stream comprising methyl formate, possibly alkali metal formate,
potassium
methoxide, methanol and possibly unreacted carbon monoxide; corresponds to
reaction mixture (Rm).
10 The invention is illustrated below with the aid of examples, without
being restricted
thereto.
The experiments on the carbonylation of methanol by means of carbon monoxide
were carried out in the laboratory apparatus shown in figure 2. A mixture of
methanol,
15 potassium methoxide and optionally an alkali metal formate was placed in
the
reservoir A. The carbonylation reactor was simulated by an HC steel autoclave
having
a volume of 270 ml. The reactor volume of the autoclave was separated by means
of
a riser tube into a 150 ml liquid phase and a 120 ml gas phase. Heating was
effected
by means of an oil bath. The temperature was regulated by means of a
thermocouple.
Methanol and the catalyst system are fed continuously from the reservoir A
into the
carbonylation reactor (B) (see stream 10 in figure 2). Carbon monoxide is fed
in via
stream 11. For analysis, a stream 12 is taken off from the carbonylation
reactor (B)
and conveyed via an on-line ATR-FIR measurement sensor back to the
carbonylation
reactor (B). The ATR-FIR measurement sensor (C) has a calibration from 0 to
80% by
weight of methyl formate in methanol. In the measurement sensor, a measurement
point was determined every 60 seconds, for which purpose the average of 64
individual measurements was formed.
The composition of the mixture comprised in the reservoir A and the
composition of
the reaction mixture (Rm) obtained in the experiments is reported in the
following
examples.
Comparative example 1
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The comparative example was carried out in the laboratory plant shown in
figure 2.
Firstly, the entire laboratory plant was made inert by means of nitrogen.
Likewise
under nitrogen, 1400 g of a solution composed of 99.2% by weight of methanol
and
0.8% by weight of potassium methoxide was made up and transferred under
nitrogen
into the reservoir (A) which stood on a balance. 555 g/h of this mixture were
pumped
continuously as stream (10) into the autoclave (B) from below. 188 standard
l/h of
carbon monoxide (purity 99.97% by volume) were fed as stream (11) into the
carbonylation reactor on the lid side. Autoclave (B) was vigorously stirred at
750 revolutions per minute and operated at 85 C. The two¨phase reaction
mixture
(Rm) is continuously discharged as stream (13) from the carbonylation reactor
via the
riser tube. The pressure in the carbonylation reactor was maintained at 55 bar
by
means of a pressure regulating valve in the discharge line. For the on-line
analysis,
801/h of the reaction mixture (Rm) were conveyed continuously as stream (12)
by
means of a pump from the carbonylation reactor. Stream (12) was cooled to 30
C,
subsequently pumped through an ATR-FIR sensor (C) and from there conveyed back
into the carbonylation reactor. After 1 hour, a steady-state methyl formate
content in
the reactor of 10.5% by weight was measured.
Example 2
Example 2 was carried out in a manner analogous to comparative example 1. As
feed,
1400 g of a solution composed of 96.7% by weight of Me0H, 0.8% by weight of
potassium methoxide and 2.5% by weight of potassium formate were introduced
under nitrogen into reservoir (A). The experimental procedure and the
experimental
parameters were analogous to comparative example 1. After 1 hour of carrying
out the
experiment, a steady-state methyl formate content in the reactor of 12.8% by
weight
was measured.
It can be seen from example 2 that the formation of methyl formate can be
increased
by 22% under otherwise identical reaction conditions by use of 2.5% by weight
of
potassium formate in the feed.
Example 3
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Example 3 was carried out in a manner analogous to comparative example 1. As
feed,
1400 g of a solution composed of 94.2% by weight of Me0H, 0.8% by weight of
potassium methoxide and 5.0% by weight of potassium formate were introduced
under nitrogen into reservoir (A). The experimental procedure and the
experimental
parameters selected were analogous to comparative example 1. After 1 hour of
carrying out the experiment, a steady-state methyl formate content in the
reactor of
13.3% by weight was measured.
It can be seen from example 3 that the formation of methyl formate can be
increased
further compared to example 2 under otherwise identical reaction conditions by
use of
5% by weight of potassium formate.
Comparative example 4
Comparative example 4 was carried out in the laboratory plant shown in figure
2.
Firstly, the entire laboratory plant was made inert by means of nitrogen.
Likewise
under nitrogen as protective gas, 850 g of a solution composed of 99.3% by
weight of
methanol and 0.7% by weight of potassium methoxide was made up and transferred
under nitrogen into the reservoir (A) which stood on a balance. 480 g/h of
this mixture
were pumped continuously as stream (10) into the autoclave (B) from below. 155
standard l/h of carbon monoxide (purity 99.97% by volume) were fed as stream
(11)
into the- carbonylation reactor on the lid side. Autoclave (B) was vigorously
stirred at
750 revolutions per minute and operated at 85 C. The two¨phase reaction
mixture
(Rm) is continuously discharged as stream (13) from the carbonylation reactor
via the
riser tube. The pressure in the reactor was maintained at 55 bar by means of a
pressure regulating valve in the discharge line. For the on-line analysis, 80
l/h of the
reaction mixture (Rm) were conveyed continuously as stream (12) by means of a
pump
from the carbonylation reactor (B). Stream (12) was cooled to 30 C,
subsequently
pumped through an ATR-FIR sensor (C) and from there conveyed back into the
carbonylation reactor (B). After 1 hour, a steady-state methyl formate content
in the
reactor of 11.6% by weight was measured.
Example 5
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Example 5 was likewise carried out in the laboratory plant shown in figure 2.
As feed,
850 g of a solution composed of 94.3% by weight of Me0H, 0.7% by weight of
potassium methoxide and 5.0% by weight of sodium formate were introduced under
nitrogen into the reservoir (A). The experimental procedure and the
experimental
parameters selected were analogous to comparative example 4. After 1 hour of
carrying out the experiment, a steady-state methyl formate content in the
reactor of
13.0% by weight was measured.
Example 6
Example 6 was likewise carried out in the laboratory plant shown in figure 2.
As feed,
850 g of a solution composed of 94.3% by weight of Me0H, 0.7% by weight of
potassium methoxide and 5.0% by weight of potassium formate were introduced
under nitrogen into the reservoir (A). The experimental procedure and the
experimental parameters selected were analogous to comparative example 4.
After
1 hour of carrying out the experiment, a steady-state methyl formate content
in the
reactor of 15.2% by weight was measured.
Example 7
Example 7 was likewise carried out in the laboratory plant shown in figure 2.
As feed,
850 g of a solution composed of 94.3% by weight of Me0H, 0.7% by weight of
potassium methoxide and 5.0% by weight of rubidium formate were introduced
under
nitrogen into reservoir (A). The experimental procedure and the experimental
parameters selected were analogous to comparative example 4. After 1 hour of
carrying out the experiment, a steady-state methyl formate content in the
reactor of
13.6% by weight was measured.
It can be seen from examples 5 to 7 that the formation of methyl formate can
be
significantly increased compared to comparative example 4 under otherwise
identical
reaction conditions by addition of 5% by weight of sodium formate, potassium
formate
and rubidium formate. However, the use of potassium formate is preferred
(example
6).
