Discovered in 1938, hydroformylation is one of the most important reactions using homogeneous precious metal catalysts. In the process, olefins react to aldehydes using hydrogen and carbon monoxide (synthesis gas). The main problem for the sensitive and expensive catalyst system, however, is the downstream processing of the reaction products, typically done by thermal separation, by which the catalyst system deactivates and is lost by clustering. In contrast, organophilic nanofiltration allows the catalyst to be separated under stabilizing conditions in a gentle and also energy saving way. As a first step to an integrated membrane reactor concept for homogeneous catalysis, two different membranes and the influence of CO on the separation were investigated for the Rh catalysed hydroformylation of octene and dodecene as examples. Catalyst rejections in excess of 99% in a single stage membrane separation combined with a high CO partial pressure that prevents the catalyst from deactivation and losses through the formation of clusters during the separation shows that organophilic nanofiltration can be a benchmark setting separation technology in homogeneous catalysis. (C) 2010 Elsevier B.V. All rights reserved.