Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-05-31
2002-09-03
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S454000, C422S224000
Reexamination Certificate
active
06444856
ABSTRACT:
The present invention relates to a process for preparing aldehydes and/or alcohols having from 6 to 30 carbon atoms by hydroformylation of olefins by means of synthesis gas in the presence of a cobalt catalyst at from 120 to 210° C. and pressures of from 100 to 400 bar, in which a reaction mixture comprising olefins, synthesis gas and catalyst or catalyst precursor, preferably aqueous cobalt salt solution, is introduced at high velocity into a high-pressure reactor. A liquid phase which, for example, consists of not yet reacted reaction mixture and aldehydes which have already been formed is present in the high-pressure reactor. In addition, the present invention relates to an improved hydroformylation reactor for preparing aldehydes and/or alcohols which comprises a high-pressure tube having at least one inlet nozzle for a reaction mixture and at least one outlet line for reaction products.
The hydroformylation of olefins by means of carbon monoxide and hydrogen in the presence of metal carbonyls of transition group VIII of the Periodic Table, for example cobalt or rhodium compounds, to form aldehydes having one more carbon atom is referred to as the oxo process. The aldehydes obtained in this way can be converted into the corresponding alcohols by subsequent hydrogenation. The oxo process is a widespread industrial method of preparing aldehydes and alcohols. A person skilled in the art therefore has a wide choice of proven methods of carrying out the oxo process (cf. J. Falbe, editor, “New Synthesis with Carbon Monoxide”, Springer-Verlag, Berlin 1980). While lower olefins are now hydroformylated using virtually exclusively ligand-modified rhodium or cobalt catalysts, for example rhodium catalysts modified with phosphines, the oxo process using unmodified cobalt or rhodium catalysts still retains its dominant position in the reaction of higher olefins (i.e. olefins having more than 6 carbon atoms).
With the exception of unbranched olefins in the case of which retention of the linear structure in the hydroformylation is of great importance for the end products, the branched olefins which are readily obtainable by oligomerization of C
3
- and/or C
4
-olefins are hydroformylated industrially virtually exclusively by means of unmodified cobalt carbonyls, i.e. in the absence of ligands. This catalyst system is not only very cheap, but is also universally usable. Furthermore, compared to rhodium catalsyts, cobalt catalysts give higher yields of the particularly sought-after linear aldehydes starting from the same olefin.
The reaction of olefins with carbon monoxide and hydrogen to form aldehydes and alcohols proceeds exothermically. When this reaction is carried out continuously on an industrial scale, it is therefore necessary to take steps to ensure that the heat of reaction is distributed uniformly in the reaction mixture and removed. Local temperature peaks, which lead to undesirable secondary and subsequent reactions, have to be substantially avoided. In addition, it has to be ensured that the liquid starting materials are well mixed with the gaseous starting materials so that the reaction proceeds in the stoichiometric ratio.
The processes which are used industrially at present differ essentially in the form in which the cobalt carbonyls are made available to the hydroformylation reactor and the way in which the catalyst is removed from the reaction mixture after the hydroformylation and is returned to the process with very small losses.
A proven method is the use of aqueous solutions of cobalt salts of lower carboxylic acids, preferably cobalt formate or cobalt acetate. Under the conditions prevailing in the reactor, the Co(II) salts are rapidly converted into the actual hydroformylation catalyst, namely hydridocobalt tetracarbonyl (HCo(CO)
4
). The hydroformylation occurs in a high-pressure reactor in which an intimate mixture of olefin, catalyst complex and synthesis gas is present at from 120 to 210° C. and pressures of from 100 to 400 bar. After the olefin has been reacted, the cobalt carbonyls homogeneously dissolved in the organic phase can be converted back into Co(II) compounds by a valence change on the central atom by means of oxidizing substances and thus made heterogeneous. The Co(II) compounds are extracted from the organic reaction product using a weakly acidic, aqueous phase, so that after phase separation the organic phase is virtually cobalt-free and can be passed directly to further processing.
The aqueous solution of cobalt salts can, with or without prior concentration, be returned directly as catalyst precursor to the high-pressure reactor or be used as uptake medium in the oxidation of the output from the reactor.
Processes in which the preparation of the catalyst complex, known as precarbonylation, the extraction of the resulting catalyst complex from the aqueous phase into the organic, olefin-containing phase and the hydroformylation of the olefin are carried out in separate process steps are known. Less complicated in terms of apparatus and therefore more economical is a single-stage process in which the formation of the catalytically active cobalt carbonyls from the aqueous cobalt salt solution and the hydroformylation of the feed olefin are carried out directly in the high-pressure reactor in a type of single-vessel reaction. The presence of aqueous phase in the reactor has the effect of increasing the yield, since subsequent reactions of the aldehydes initially formed, e.g. acetal formation or enal formation, are suppressed. As a result, no additional work-up steps for redissociating undesirable high boilers are necessary.
Among the prerequisites for an effective single-stage oxo process in a high-pressure reactor are that, firstly, the aqueous cobalt salt solution is dispersed very finely in the liquid olefin and that, secondly, intimate mixing with the synthesis gas introduced takes place.
Against the background of these conditions, DE 1 205 514 A describes a process in which at least part of the reactants are introduced at high velocity into a high-pressure reactor via a plurality of nozzles. The high-pressure reactor has a tubular construction and in its interior has internals, for example guide tubes, which make circulation of the reaction mixture possible. The circulation is maintained by the momentum of the reactants injected into the reaction mixture. According to DE 1 205 514 A, starting olefin and catalyst solution are injected. DE 1 938 102 A describes a similar process in which the reactants, i.e. the gaseous starting materials, the starting olefin and the catalyst solution are introduced through a single nozzle into the reaction product circulating in the high-pressure reactor. Here, the reactants are introduced into a mixing zone which is arranged in a cascade-like fashion in the reaction zone and extends in the entry direction of the reactants. The mixing zone can be realized by means of cylindrical or cone-shaped reactor internals having a defined diameter/length ratio. It allows a higher olefin throughput without losses in conversion and, owing to the good mixing, leads to smaller temperature gradients and therefore to reduced high boiler formation.
DE 1 938 102 A proposes introducing the reaction mixture into the high-pressure reactor at a nozzle exit velocity of from 10 to 100 m/s, in particular from 10 to 60 m/s. However, fluctuations in the feed streams, i.e. the introduction of the reaction mixture into the reactor, can occur in operation. The causes of these can be changed external circumstances, for instance nonuniform acceptance of aldehyde or alcohol on the part of the plant carrying out further processing. In addition, other starting olefins can make a change in the throughput necessary.
To be able to maintain the preferred nozzle exit velocity of from 10 to 60 m/s even when the throughput changes, part of the contents of the reactor are recirculated to the feed stream by means of an external circulation pump in the process described in DE 1 938 102 A. Under the conditions prevailing in the high-pressure oxo process usi
Borchert Gerhard
Fröhlich Hans-Jürgen
Grenacher Armin Volker
Hein Hans-Georg
Schönmann Willi
BASF - Aktiengesellschaft
Keil & Weinkauf
Padmanabhan Sreeni
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