The rhodium–BIPHEPHOS catalysed hydroformylation of trans-4-octene yields n-nonanal at high selectivity under mild reaction conditions. In this contribution a new method for an efficient product and catalyst separation in hydroformylation reactions is presented. By application of a temperature-dependent multi-component solvent (TMS) system, classical extraction process steps can be omitted and catalyst leaching reduced. The Hansen solubility parameter concept of solvent selection is presented to determine in general TMS systems for homogeneous catalysed reactions.