Note: Descriptions are shown in the official language in which they were submitted.
CA 02311589 2000-OS-24
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METHOD FOR HYDROGENATING CARBOXYLIC ACIDS OR THE
ANHYDRIDES OR ESTERS THEREOF INTO ALCOHOL
Description
The invention relates to a process for increasing the catalytic
activity and avoiding secondary reactions in the hydrogenation of
carboxylic acids or derivatives thereof by adding specific basic
alkali metal compounds or alkaline earth metal compounds to the
hydrogenation feed.
It is known to use basic components during the preparation of
hydrogenation catalysts. A certain amount of these components is
then still present on the finished catalyst. For example,
EP-A 528 305 describes the preparation of a Cu/Zn0/A1203 catalyst
in which basic compounds, such as alkali metal carbonates, alkali
metal hydroxides or alkali metal hydrogencarbonates, are used
during precipitation of the catalyst constituents. A small amount
of the alkali metal additive then remains in the catalyst.
Another example of preparing alkali metal-containing catalysts is
described in DE-A 2 321 101, in which Co-containing catalysts are
prepared. EP-A 552 463 describes the preparation of Cu/Mn/A1
catalysts which, owing to their preparation, may likewise contain
small amounts of alkali metal.
The resulting hydrogenation catalysts contain the alkali metal
uniformly distributed throughout the whole catalyst composition.
However, since only the outer or accessible surface of the
catalyst is catalytically active, the amount of alkali metal at
these sites is very small and is generally washed out quickly by
the stream to be hydrogenated since the alkali metal is not
bonded covalently, but is present only in a loosely bonded form.
In addition, the introduction of compounds which are able to
acidify the catalyst rapidly exhausts the capacity of the basic
centers produced by the alkali metal. As a result, reactions
which are promoted by acid catalysis, such as etherifications or
dehydrations, may lessen the selectivity of hydrogenation to
alcohols. In general, the introduction of compounds which acidify
the catalyst sometimes severely shortens the service life of the
catalyst since the structure of the catalyst surface changes, for
example as a result of catalyst constituents being washed out or
recrystallization of the active metals.
~~5~/48644 CA 02311589 2000-OS-24
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Accordingly, the hydrogenation catalysts are sometimes sensitive
to the hydrogenation feed itself or to impurities which are
present in the hydrogen used or in the hydrogenation feed. Thus,
many catalysts in the hydrogenation of carboxylic acids are, for
example, not only acidified, but also severely damaged chemically
as a result of catalyst components being washed out. Even if the
feed material does not contain any carboxylic acids, but, for
example, contains esters, the carboxylic acids are usually
liberated by hydrolysis of the esters by traces of water. Another
problem concerns impurities, for example organic halogen
compounds, which may be introduced into the hydrogenation, for
example with the hydrogen, and have adverse effects even when the
contents of these substances are below 1 ppm. Thus, it is known
that, for example, Cu catalysts can be used to remove traces of
_ 15 halogen from feed streams by chemisorption (US 5,614,644).
Without such a preabsorption, the halogen is absorbed on the
hydrogenation catalyst, where it leads firstly to acidification
and secondly to structural modifications of the catalyst.
Accordingly, the technical solution to the problem described
typically involved the upstream installation of a "guard bed", in
which undesired impurities were absorbed. This cannot of course
remove the acids involved in the reaction, such as the carboxylic
acids which form or are used as hydrogenation feed.
It is an object of the present invention to propose a process by
means of which the catalyst-impairing effect of the acids
involved in the reaction and also of the impurities introduced
can be reduced or eliminated.
we have found that this object is achieved by a process for the
catalytic hydrogenation of carboxylic acids or anhydrides or
esters thereof to alcohols on heterogeneous catalysts which
comprise or consist of hydrogenating elements from groups 6, 7,
8~ 9, 10 and 11 and, where appropriate, from groups 2, 14 and 15
of the Periodic Table of the Elements, in the liquid phase at
from 100 to 300°C and from 10 to 300 bar, which comprises adding
from 1 to 3000 ppm, in particular from 3 to 1000, preferably from
5 to 600 ppm, based on the liquid hydrogenation feed, of a basic
alkali metal compound or alkaline earth metal compound selected
from the group consisting of hydroxides, carbonates, carboxylates
and alkoxides to the hydrogenation reaction mixture.
DE 1 235 879, Example 16, discloses the addition of trisodium
phosphate to the hydrogenation feed. This example describes the
hydrogenation of a carboxylic acid mixture which comprises 0.1a
by weight of Na3P04, inter alia adipic acid, glutaric acid,
0050/48644 CA o2311s89 2000-os-24
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succinic acid and 6-hydroxycaproic acid, a carboxyl acid mixture
which has already been hydrogenated, and also an undefined amount
of "crude monoalcohols" whose water content has been adjusted to
7%. The sole addition of Na3P04 to the hydrogenation feed is not,
however, a suitable measure for increasing the catalyst activity
and service life. After a short time in the presence of
acidifying constituents in the reaction mixture there is a
drastic drop in activity.
Carboxylic acids and derivatives may be carboxylic acids
themselves and esters, and also internal esters, i.e. lactones,
and anhydrides thereof. Examples thereof are acetic esters,
propionic esters, hexanoic esters, dodecanoic esters,
pentadecanoic esters, hexadecanoic esters,
2-cyclododecylpropionic esters, esters of glycerol with fatty
acids, malefic diesters, succinic diesters, fumaric diesters,
glutaric diesters, dimethyl adipates, 6-hydroxycaproic esters,
cyclohexanedicarboxylic diesters, benzoic esters, butyrolactone,
caprolactone, malefic acid, succinic acid, itaconic acid,
adipic
acid, 6-hydroxycaproic acid, cyclohexanedicarboxylic acid,
benzoic acid, malefic anhydride and succinic anhydride. Preferred
starting materials are diesters, in particular diesters of
low
molecular weight alcohols with dicarboxylic acids having
from 4
to 6 carbon atoms.
Suitable basic compounds are especially alkali metal hydroxides
and alkaline earth metal hydroxides, such as LiOH, NaOH,
KOH,
RbOH, CsOH, Mg(OH)2, Sr(OH)2 or Ba(OH)z. The alkali metals
or
alkaline earth metals may also be in the form of carboxylates,
, e.g. as formate, acetate, propionate, maleate or glutarate,
or as
f alkoxides, such as methoxide, ethoxide or propoxide. Carbonates
are also suitable. The basic compounds should always dissolve
homogeneously in the hydrogenation feed. If this cannot to
be
ensured, it is also possible to introduce the basic compound
in a
suitable solvent as a separate stream into the hydrogenation
itself or into the hydrogenation feed. The amounts of alkali
metal or alkaline earth metal, based on the hydrogenation
stream,
are very low, being between 1 and 3000 ppm, preferably between
3 and 1000 ppm, particularly preferably between 5 and 600
ppm.
The basic component is preferably introduced continuously.
Batchwise addition is, however, also possible. Within a short
time, it is also possible for greater amounts of basic components
than 3000 ppm, based on the hydrogenation feed, to enter
the
hydrogenation. On average, the amounts are, however, below
3000 ppm.
0050/48644 CA 02311589 2000-OS-24
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It is surprising that even after prolonged addition of the basic
components, there are no deposits on the catalyst.
The hydrogenation takes place in the liquid phase. It is not
important whether, in the case of fixed-bed catalysts, an upward
or downward flow method is chosen. Hydrogenation using suspended
catalysts is also possible.
The hydrogenation catalysts which may be used in the novel
process are generally heterogeneous catalysts suitable for the
hydrogenation of carbonyl groups. Examples thereof are described,
for example, in Houben-Weyl, Methoden der Organischen Chemie,
Volume IV/1c, pp. 16 to 26.
Of these hydrogenation catalysts, preference is given.to those
which comprise one or more elements from groups 6, 7, 8, 9, 10
and 11 and, where appropriate, from groups 2, 14 and 15 of the
Periodic Table of the Elements, in particular copper, chromium,
rhenium, cobalt, rhodium, nickel, palladium, iron, platinum,
indium, tin and antimony. Particular preference is given to
catalysts which comprise copper, cobalt, palladium, platinum or
rhenium.
Suitable catalyts are especially unsupported catalysts. In the
great majority of cases, the catalytically active metals are not
on carrier materials. Examples thereof are Raney catalysts, e.g.
based on Ni, Cu or cobalt. Other examples are Pd black, Pt black,
Cu sponge, or alloys or mixtures of, for example, Pd/Re, Pt/Re,
Pd/Ni, Pd/Co or Pd/Re/Ag.
The catalysts employed in the novel process may also be, for
example, precipitated catalysts. Catalysts of this type can be
prepared by precipitating their catalytically active components
from solutions of salts thereof, in particular from solutions of
their nitrates and/or acetates, for example by adding solutions
of alkali metal hydroxide and/or alkaline earth metal hydroxide
and/or alkali metal carbonate and/or alkaline earth metal
carbonate, e.g. as sparingly soluble hydroxides, oxide hydrates,
basic salts or carbonates, then drying the resulting precipitates
and subsequently converting them by calcination at, in general,
from 300 to 700°C, in particular from 400 to 600°C, into the
corresponding oxides, mixed oxides and/or mixed valency oxides,
which are reduced, and converted into the actual catalytically
active form by treatment with hydrogen or hydrogen-containing
gases, generally at from 50 to 700°C, in particular from 100 to
400°C, to give the corresponding metals and/or oxides in a lower
0050/48644 CA o2311s89 2000-os-24
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oxidation state. This reduction is generally continued until
water is no longer formed. To prepare precipitated catalysts
comprising a carrier material, the catalytically active
components can be precipitated in the presence of the
corresponding carrier material. However, it is also advantageous
for the catalytically active components to be precipitated
simultaneously with the carrier material from the relevant
salt
solutions. Preferred hydrogenation catalysts in the novel
process
are those comprising the hydrogenation-catalyzing metals
or metal
compounds deposited on a carrier material. Apart from the
abovementioned precipitated catalysts, which also comprise
a
carrier material in addition to the catalytically active
components, suitable supported catalysts for the novel process
are, in general, those in which the components catalyzing
the
hydrogenation have been applied to a carrier material, for
example by impregnation.
The way in which the catalytically active metals are applied
to
the carrier is generally not critical and can be brought
about in
various ways. The catalytically active metals can be applied
to
these carrier materials by for example impregnation with
solutions or suspensions of the salts or oxides of the
corresponding elements, drying and subsequent reduction of
the
metal compounds to the corresponding metals or compounds
in a
lower oxidation state by means of a reducing agent, preferably
using hydrogen or complex hydrides. Another potential way
of
applying the catalytically active metals to these carriers
consists in impregnating the carriers with solutions of salts
which readily undergo thermal decomposition, e.g. with nitrates,
or complex compounds which readily undergo thermal decomposition,
.
, e.g. carbonyl or hydrido complexes of the catalytically active
metals, and heating the carrier impregnated in this way to
from
300 to 600C for thermal decomposition of the adsorbed metal
compounds. This thermal decomposition is preferably carried
out
under a protective gas atmosphere. Examples of suitable
protective gases are nitrogen, carbon dioxide, hydrogen and
the
inert gases. The catalytically active metals can furthermore
be
deposited on the catalyst carrier by vapor deposition or
by flame
spraying. The content of the catalytically active metals
in these
supported catalysts is in principle not critical for the
success
of the novel process. However, higher contents of catalytically
active metals generally result in higher space-time conversions
than lower contents. In general, the supported catalysts
used
comprise from 0.1 to 90% by weight, preferably from 0.5 to
40o by
weight, of catalytically active metals, based on the entire
catalyst. Since these contents refer to the entire catalyst
including carrier material, but the different carrier materials
0050/48644 CA 02311s89 2000-os-24
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have very different specific gravities and specific surface
areas, lower or higher contents than these are also possible
without this having a disadvantageous effect on the result of the
novel process. It is, of course, also possible to apply a
plurality of catalytically active metals to the particular
carrier material. Furthermore, the catalytically active metals
can be applied to the carrier by for example the process of
DE-A 2 519 817, EP-A 1 477 219 and EP-A 285 420. The
catalytically active metals are present in the catalysts
disclosed in the abovementioned publications as alloys which are
produced by thermal treatment and/or reduction after, for
example, impregnation with a salt or complex of the
abovementioned metals.
Activation both of the precipitated catalysts and of the
supported catalysts can also take place in situ at the start of
the reaction by the hydrogen which is present, but these
catalysts are preferably activated separately before being used.
Suitable carrier materials are generally the oxides of aluminum
and titanium, zirconium dioxide, silicon dioxide, clays, such
as
montmorillonites, silicates, such as magnesium or aluminum
silicates, zeolites, such as ZSM-5 or ZSM-10 zeolites, and
activated carbon. Preferred carrier materials are aluminum
oxides, titanium dioxides, silicon dioxide, zirconium dioxide
and
activated carbon. It is, of course, also possible to use mixtures
of various carrier materials as carrier for heterogeneous
catalysts which can be used in the novel process. Examples
of
heterogeneous catalysts which can be employed in the novel
process are the following:
cobalt on activated carbon, cobalt on silicon dioxide, cobalt
on
aluminum oxide, rhenium on activated carbon, rhenium on silicon
dioxide, rhenium/tin on activated carbon, rhenium/platinum
on
activated carbon, copper on activated carbon, copper/silicon
dioxide, copper/aluminum oxide, copper chromite, barium copper
chromite, copper/aluminum oxide/manganese oxide, copper/aluminum
oxide/zinc oxide, and the catalysts disclosed in DE-A 3 932
332,
US-A 3,449,445, EP-A 44 444, EP-A 147 219, DE-A 3 904 083,
DE-A 2 321 101, EP-A 415 202, DE-A 2 366 264, EP 0 552 463
and
EP-A 100 406.
Preferred catalysts comprise at least one of the metals copper,
manganese, cobalt, chromium, palladium, platinum, cobalt or
nickel, particularly preferably copper, cobalt, palladium,
platinum or rhenium. If only esters are hydrogenated, the
hydrogenation catalyst preferably comprises copper.
0050/48644 CA o2311s89 2000-os-24
For the novel process, it is generally not critical which
temperature and pressure conditions are used for the
hydrogenation.
The hydrogenation temperature is generally between 100 and 300~C
and the hydrogenation pressure is generally between 10 and
300 bar.
By metering the particular basic compounds according to the
invention, also in substoichiometric amounts, based on the
impurities introduced, it is possible to prevent, or at least
severely delay, acidification on the one hand and structural
modification of the catalyst on the other. This is evident from
an improvement in selectivity, an increase in the useful life of
the catalyst, and, in a manner which is not yet fully understood,
also by an increase in conversion.
The alcohols obtained in the hydrogenation are desired compounds,
e.g. for solvents, intermediates or precursors for plastics such
20 as polyurethanes or polyesters. The novel process is further
illustrated in the examples below, but is not limited thereto.
The reaction products were analyzed by gas chromatography.
Example 1
About 20 g/h of a 50~ ethanolic solution of ethyl
2-cyclododecylidenepropionate (prepared from ethyl
2-bromopropionate and cyclododecane), which also contained
7 ppm
of halogen (detected as C1), were hydrogenated at 220C/220
bar
over 25 ml of a Cu0 (70~) /Zn0 (25%) /A1z03 (5~S) catalyst
(precipitation of an aqueous solution of sodium aluminate
and
zinc(II) nitrite hexahydrate with aqueous sodium carbonate
solution, removal of the resulting Zn0- and A1203-containing
precipitate by filtration, slurrying of the precipitate with
an
a~eous solution containin co
g pper(II) nitrate trihydrate and
zinc(II) nitrate hexahydrate, precipitation with aqueous sodium
carbonate solution, filtration, washing, drying and calcination
of the obtained precipitate and shaping of the calcined powder
to
tablets), which had previously been activated in a stream
of
hydrogen at 180C. The content of 2-cyclododecylpropanol (musk
odor) in the hydrogenation product was 70s (calculated on
an
ethanol-free basis). The conversion after about 8 h was about
930
(selectivity 750). 50 ppm of sodium methoxide were then mixed
into the feed stream. As a result, the content of desired
product
rose to about 77~, and the conversion to 96% (selectivity
80%).
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Example 2
A mixture (prepared as in DE-A 19 607 953 in the example, steps
1-4) of predominantly dimethyl adipate and methyl
6-hydroxycaproate was hydrogenated (feed 1 kg, reactor
temperature 205 to 220C, pressure 250 bar) over 2.5 1 of a
T 4489
Cu/A1/Mn catalyst from Slid-Chemie which had previously been
activated in a stream of hydrogen at 180C. The hydrogenation
feed
contained about 1 ppm of halogen compounds (detected as Cl).
At
the start of the hydrogenation, the content of the byproduct
hexanediol diether present in the hydrogenation product was
Oo.
After 6 experiment days the ether could be detected. The ether
content rose steadily to 0.8~ by the 16th experiment day (content
of 1,6-hexanediol in the product 27~, residual contents of
dimethyl adipate 3.6~, methyl 6-hydroxycaproate 3.20). 500
ppm of
.. sodium ethoxide, based on the hydrogenation feed, dissolved
in
methanol, were then introduced into the reactor via a separate
feed. Ether was no longer formed (content of 1,6-hexanediol
in
the product 30~, residual content of dimethyl adipate 1.1~,
methyl 6-hydroxycaproate 2.60).
whilst operating without addition of Na, the content of Mn in the
hydrogenation product was 5 ppm. Whilst metering in Na, the Mn
Content fell to below 3 ppm.
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