Process for preparing aldehydes and cooling a stream of matter

A process for preparing aldehydes by hydroformylation of olefins, the process comprising:

• a) reacting C4 to C20 olefins in a hydroformylation in at least one reaction zone in the presence of a synthesis gas and a homogeneous rhodium catalyst system, at a pressure of 100 to 350 bar and a temperature of 90° C. to 250° C., to obtain a biphasic hydroformylation mixture comprising a gas phase and a liquid phase, wherein the biphasic hydroformylation mixture contains at least unconverted olefins, the synthesis gas, the homogeneous rhodium catalyst system, and aldehydes formed, which is withdrawn from the at least one reaction zone;
• b) expanding the biphasic hydroformylation mixture in a first expansion, to a pressure between 11 bar and 50 bar, and separating the biphasic hydroformylation mixture into a first gaseous phase comprising the synthesis gas, and a first liquid phase comprising the unconverted olefins, the homogeneous rhodium catalyst system, the aldehydes formed, and optionally, remaining synthesis gas;
• c) expanding the first liquid phase obtained from b) in a second expansion, to a pressure between 1 bar and 10 bar, and separating the first liquid phase into a second gaseous phase comprising the remaining synthesis gas, and a second liquid phase comprising the unconverted olefins, the homogeneous rhodium catalyst system, and the aldehydes formed;
• and
• d) feeding the second liquid phase to an at least three-stage removal,
• wherein, in the first stage, a first membrane separation is effected, in which the homogeneous rhodium catalyst system is enriched in a first retentate and a permeate is directed to the next stage;
• in the second stage, the permeate from the first membrane separation is subjected to a thermal separation in which at least a portion of the aldehydes formed is removed together with a top product, and a liquid bottom product is directed to the third stage;
• and
• in the third stage, the liquid bottom product from the thermal separation is subjected to a second membrane separation in which the homogeneous rhodium catalyst system is enriched in a second retentate,
• wherein the biphasic hydroformylation mixture prior to the first expansion in b), the first liquid phase prior to the second expansion in c), or the second liquid phase prior to the feeding to the at least three-stage removal in d) is cooled to a temperature between 40 and 100° C.