Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-02-22
2002-06-11
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S429000, C568S449000, C568S881000, C568S885000
Reexamination Certificate
active
06403836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved process for the hydroformylation of olefins in the presence of unmodified cobalt carbonyl complexes, in which the concentration of formic acid in aqueous solutions containing cobalt compounds is reduced by catalytic decomposition.
2. Discussion of the Background
Higher alcohols, in particular those having from 4 to 25 carbon atoms, may be prepared by the catalytic hydroformylation (or oxo reaction) of olefins having one less carbon atom, followed by catalytic hydrogenation of the resulting aldehyde- and alcohol-containing reaction mixtures. These alcohols may be used, for example, in preparing plasticizers and detergents.
The type of catalyst system and the optimum reaction conditions for the hydroformylation depend on the reactivity of the olefin used. The dependence of the reactivity of the olefins on their structure is described, for example, by J. Falbe, New Syntheses with Carbon Monoxide, Springer-Verlag, Berlin, Heidelberg, N.Y., 1980, page 95 ff. In particular, the differing reactivity of isomeric octenes is known (B. L. Haymore, A van Hasselt, R. Beck, Annals of the New York Acad. Sci., 415 (1983), pages 159-175).
Industrial olefin mixtures which are used as starting materials for the oxo process comprise olefin isomers having a variety of structures, for example with different degrees of branching, different positions of the double bond in the molecule and possibly also different numbers of carbon atoms. This is particularly true of olefin mixtures which have been formed by dimerization or trimerization, or further oligomerization of C
2
-C
5
olefins or other readily available higher olefins, or by cooligomerization of such olefins. For example, tripropenes and tetrapropenes and also dibutenes, tributenes and tetrabutenes are typical isomeric olefin mixtures which may be reacted by rhodium-catalyzed, or preferably cobalt-catalyzed hydroformylation reactions, to give the corresponding aldehyde and alcohol mixtures.
If alcohols having a very low degree of branching are desired, the hydroformylation reaction may preferably be carried out using unmodified cobalt catalysts. Compared to rhodium hydroformylation catalysts, cobalt hydroformylation catalysts provide higher yields of the particularly valuable oxo products having a higher content of straight chains.
The hydroformylation of olefins catalyzed by unmodified cobalt carbonyl complexes provides reaction mixtures comprising aldehydes, alcohols, their formic esters, unreacted olefins, free formic acid and additional by-products, as well as the catalyst. In order to obtain an almost cobalt-free reaction mixture suitable for further processing, the various cobalt compounds present in the hydroformylation product have to be removed. In addition, because the cobalt hydroformylation catalysts are expensive, any cobalt catalysts and catalysts residues which have been separated off should preferably be recycled.
During the hydroformylation and/or during removal of the cobalt compounds from the hydroformylation product, formic acid is formed by the hydrolysis of formic esters. The presence of formic acid inhibits the formation of active hydroformylation catalysts, for example, cobalt carbonyls, when the cobalt compounds of the hydroformylation product are regenerated to re-form active hydroformylation catalysts.
A conventional method for recovering the catalyst from the hydroformylation mixture comprises extracting cobalt compounds from the reactor output with an aqueous base, acidifying the extract to liberate HCo(CO)
4
, and returning the HCo(CO)
4
to the hydroformylation reactor (Kuhlmann process). However, a disadvantage of this process is that one must dispose of the by-product salt of the base used to extract the cobalt compounds from the reactor output.
GB 2055371 describes a process comprising the following steps:
a) A portion of the cobalt carbonyls present in the hydroformylation product is reacted with an aqueous cobalt(II) salt solution to form Co{Co(CO)
4
}
2
. At the same time, the cobalt complex salt is extracted into the aqueous phase.
b) In a second step, the remaining cobalt carbonyls are oxidized with oxygen in the presence of an aqueous acid to give cobalt(II) salts. The aqueous extract thus formed is recycled to step a), above.
c) The active cobalt compounds, i.e. the cobalt hydroformylation catalyst, are prepared by reaction of the extract of step (a) with synthesis gas in the presence of an organic solvent.
A disadvantage of this process is that the separation of the cobalt compounds from the hydroformylation product, alone, requires an oxidation step and two phase separations.
WO 93/24437 describes a process for catalyst removal and regeneration, which essentially comprises the following steps:
a) After reducing the pressure of the hydroformylation output, the cobalt compounds are extracted with an aqueous solution having a pH of not more than 7, in particular an aqueous solution comprising formic acid, under either reductive conditions, or oxidative conditions (e.g., in the presence of oxygen).
If oxidative extraction conditions are employed, the following work-up procedure is used:
b) The aqueous extract comprising the cobalt compounds is concentrated by distillation. The top product (i.e., the lower density phase) is a mixture of water and acids (formic acid), part of which is recycled back to the extraction step a).
c) The aqueous concentrate from step b) is reacted with synthesis gas at elevated temperature at greater than atmospheric pressure to give a mixture comprising cobalt carbonyls.
d) The cobalt carbonyls are then stripped from the mixture obtained from step c). The remaining aqueous stream is recirculated back to step a).
e) The cobalt carbonyls are extracted from the stripping gas using the olefin starting material (for the hydroformylation).
In the nonoxidative work-up, the same process steps are carried out, but in a different order (a-d-c-b) and with the further difference that the largely cobalt-free aqueous stream from step d) is divided into two substreams which are recirculated to steps a) and b).
WO 93/24438 and U.S. Pat. No. 5,321,168 describe further developments of the process disclosed in WO 93/24437. In the same sequence of work-up steps, a palladium catalyst is additionally used for catalyst preformation (step c). In addition, U.S. Pat. No. 5,321,168 describes regenerating the activity of the palladium catalyst.
All of these work-up methods are very complex and incur high capital and operating costs.
An additional process is described in J. Falbe, New Syntheses with Carbon Monoxide, Springer-Verlag, Berlin, Heidelberg, N.Y., 1980, page 164, 165 (BASF process) and comprises the following steps:
a) Oxidation of the cobalt carbonyls by oxygen in the presence of acids, in particular formic acid formed in the process, to give cobalt(II) salts, followed by their extraction from the hydroformylation mixture.
b) Reduction of the cobalt(II) salts in the aqueous extract from step a) in the presence of an organic solvent to give cobalt carbonyls.
c) Extraction of the cobalt carbonyls into an organic phase, preferably the starting olefin, which is then fed into the hydroformylation reactor.
DE 196 54 340 describes a lower capital and operating cost hydroformylation process in which steps b) and c) are carried out in situ in the hydroformylation reactor. The space-time yields of this process also depend on the formation and stability of the catalyst complex in the hydroformylation reactor. The space-time yield may be further improved.
In all of the conventional processes described above, the formic acid concentration is established by the reaction conditions, and is generally neither influenced nor controlled at all, or is reduced by a further process step such as distillation.
It is therefore an object of the invention to develop a hydroformylation process for olefins which has a closed cobalt catalyst circuit which simplifies catalyst recirculation and provides for high space-
Bueschken Wilfried
Gosmann Felix
Kaizik Alfred
Toetsch Walter
Oxeno Olefinchemie GmbH
Padmanabhan Sreeni
LandOfFree
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