| abstract |
The invention relates to processes for the preparation of aldehydes by hydroformylation of alkenes, in which an alkene-containing feed mixture is subjected to a primary hydroformylation with synthesis gas in the presence of a homogeneous catalyst system, wherein the primary hydroformylation takes place in a primary reaction zone, from which continuously a cycle gas containing at least a portion the products, and unreacted starting materials of the primary hydroformylation withdrawn and partially condensed, wherein non-condensed portions of the recycle gas are returned to the primary reaction zone, and condensed portions of the recycle gas are separated by distillation in an aldehyde separation in a mixture rich in aldehyde and in a low-aldehyde mixture , It is based on the task of further developing the process in such a way that it achieves high sales even in the case of a deteriorating raw material situation and aldehyde in good product quality. In particular, a solution should be found to reinforce existing oxo plants for the recovery of inferior sources of raw materials. This object is achieved in that the low aldehyde mixture is separated by means of a membrane separation unit in a retentate and in a permeate such that aldehydes contained in the aldehyde mixture are enriched in the permeate while alkane contained in the low aldehyde mixture are enriched in the retentate. The alkene-rich permeate is then transferred to a secondary reaction zone where it is subjected to secondary hydroformylation with syngas in the presence of a SILP catalyst system. The reaction product obtained from the secondary hydroformylation is recycled to the aldehyde separation. |