Process for preparing aldehydes in the presence of an...

Details Process for preparing aldehydes in the presence of an... Process for preparing aldehydes in the presence of an...

1999-08-30

2001-08-14

Padmanabhan, Sreeni (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S451000

Reexamination Certificate

active

06274774

ABSTRACT:

The present invention relates to a process for preparing aldehydes by reacting olefinic compounds having from 6 to 16 carbon atoms with hydrogen and carbon monoxide at superatmospheric pressure in the presence of an aqueous phase comprising rhodium and sulfonated triarylphosphines as catalyst.
It is known that aldehydes and alcohols can be prepared by reacting olefins with carbon monoxide and hydrogen. The reaction is catalyzed by hydrido-metal carbonyls, preferably those of metals of group VIII of the Periodic Table. Besides cobalt, which is widely used industrially as catalyst metal, rhodium has for some time achieved increasing importance. In contrast to cobalt, rhodium allows the reaction to be carried out at low pressure; in addition, straight-chain n-aldehydes are preferentially formed and iso-aldehydes are formed to only a subordinate extent. Finally, significantly less hydrogenation of the olefins to saturated hydrocarbons occurs when using rhodium catalysts than when using cobalt catalysts.
In the processes which have been introduced in industry, the rhodium catalyst is used in the form of modified hydrido-rhodium carbonyls which contain additional ligands which may, if appropriate, be used in excess. Tertiary phosphines or phosphites have been found to be particularly useful as ligands. Their use makes it possible to reduce the reaction pressure to below 30 MPa.
However, the separation of the reaction products and the recovery of the catalysts homogeneously dissolved in the reaction product create problems in this process. In general, the reaction product is distilled from the reaction mixture. In practice however, owing to the thermal sensitivity of the aldehydes and alcohols formed, this method can only be employed in the hydroformylation of lower olefins, i.e. olefins having up to about 5 carbon atoms in the molecule.
The hydroformylation of long-chain olefins or olefinic compounds containing functional groups forms products having a high boiling point and these cannot be separated from the homogeneously dissolved rhodium complex catalyst by distillation. The thermal stressing of the material being distilled leads to considerable losses of desired products due to thick oil formation and of catalyst due to decomposition of the rhodium complexes.
The separation of the catalyst by thermal means is avoided by use of water-soluble catalyst systems. Such catalysts are described, for example, in DE-C 26 27 354. The solubility of the rhodium complexes is here achieved by use of sulfonated triarylphosphines as constituent of the complex. In this process variant, the catalyst is separated from the reaction product after the hydroformylation reaction is complete simply by separating the aqueous and organic phases, i.e. without distillation and thus without additional thermal process steps. A further feature of this procedure is that n-aldehydes are formed with high selectivity from terminal olefins and iso-aldehydes are formed to only a very subordinate extent. Apart from sulfonated triarylphosphines, carboxylated triarylphosphines are also used as constituents of water-soluble rhodium complexes.
The use of water-soluble catalysts has been found to be useful in the hydroformylation of lower olefins, in particular ethylene and propene. However, if higher olefins such as hexene, octene or decene are used, the reaction rate is greatly reduced. An industrial-scale reaction is no longer economical when using olefins having six or more carbon atoms.
In order to increase the conversion and/or the selectivity of the reaction to n-aldehydes in the hydroformylation of higher olefins by means of water-soluble catalysts, the addition of an amphiphilic reagent (DE 31 35 127 A1) or a solubilizer (DE 34 12 335 A1) has been recommended.
According to both DE 31 35 127 A1 and DE 34 12 335, very high conversions are obtained using quaternary ammonium salts which have a long-chain alkyl radical, while nonionic substances based on polyethylene glycol lead to comparatively low conversions.
As can be seen from Table 7 in DE 31 35 127, the hydroformylation of 1-dodecene by means of rhodium and monosulfonated triphenylphosphine (3-Ph
2
PC
6
H
4
SO
3
Na) without addition of an amphiphilic reagent leads to a conversion of 56% (Example 77), while the addition of C
12
H
25
(OCH
2
CH
2
)
23
OH (=“Brij 35”) leads to a reduction in the conversion to 37% (Example 78).
According to DE 34 12 335 (Table 4), the hydroformylation of hexene by means of rhodium and trisodium tri(m-sulfophenyl)phosphine without addition of a solubilizer leads to a conversion of 36% (Example 10), while addition of 2.5% of triethylene glycol (Example 14) or 5% of polyglycol 200 (Example 11) gives a conversion of 43.5% or 43% respectively. The addition of the solubilizer results in no significant increase in the conversion, and increasing the amount of solubilizer from 2.5% to 5% also does not increase the conversion. On the other hand, a very high conversion, namely 86%, is achieved with an addition of 2.5% of trimethylhexadecylammonium bromide.
However, the use of quaternary ammonium salts as amphiphilic reagent or solubilizer is not without problems because of the poor biodegradability of these compounds. Thus, the presence of quaternary ammonium salts in wastewater leads to difficulties in wastewater treatment.
Amphiphilic reagents and solubilizers serve to aid mass transfer between the individual phases and thus the miscibility of aqueous catalyst phase and organic phase. An increase in the miscibility of aqueous catalyst phase and organic phase means an increased solubility of the organic phase in the aqueous phase and of the aqueous phase in the organic phase. In this way, increasing amounts of amphiphilic reagent and solubilizer and also rhodium and water-soluble phosphine can get into the organic phase and be carried off with the organic phase after phase separation.
Furthermore, it is to be expected that with increasing miscibility of aqueous catalyst phase and organic phase the demixing required for phase separation will no longer take place to a sufficient extent, if at all, as a result of the formation of emulsions or solutions. A corresponding increase in the miscibility is to be expected particularly when the amount of amphiphilic reagents and solubilizers added is increased.
Increased discharge of rhodium, water-soluble phosphine and amphiphilic reagent or solubilizer via the organic phase is, like reduced demiscibility of the phases, undesirable, since the rhodium, water-soluble phosphine and amphiphilic reagent or solubilizer should remain in the aqueous catalyst phase and good demiscibility is an essential prerequisite for the separation of organic and aqueous phases which is necessary at the end of the hydroformylation.
In view of the above considerations, there is a need for a process which avoids the abovementioned disadvantages and, in addition, can be implemented industrially in a simple manner.
This object is achieved by a process for preparing aldehydes. It comprises reacting an olefinically unsaturated compound having from 6 to 16 carbon atoms with hydrogen and carbon monoxide at from 20 to 170° C. and from 1 to 300 bar in the presence of an aqueous phase comprising rhodium and sulfonated triarylphosphines as catalyst and from 10 to 70% by weight of a compound of the formula (1) R(OCH
2
CH
2
)
n
OR
1
, where, in the formula (1), R is hydrogen, a straight-chain or branched alkyl radical having from 1 to 4 carbon atoms or a hydroxyalkyl radical having from 1 to 4 carbon atoms, R
1
is hydrogen or a methyl radical, in particular hydrogen, and n is an integer from 3 to 50.
In view of the abovementioned findings of DE 34 12 335 (Table 4, Examples 10, 14 and 11) and DE 31 35 127 (Table 7, Examples 77 and 78), it was not to be expected that addition of compounds of the formula (1) R(OCH
2
CH
2
)
n
OR
1
in the abovementioned amounts would lead to a significant increase in the conversion and at the same time to a high selectivity in respect of the formation of n-aldehydes.
It is also surprising that the addi

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