The invention relates to a method for enriching a homogenous catalyst from a process flow comprising said homogenous catalyst as a component, wherein the process flow is conducted over at least one membrane and wherein the membrane wholly or partially comprises a polymer that has planar polymer units connected to one another via a rigid link and wherein the linker is contorted, such that at least one planar polymer unit is connected to at least one second planar polymer unit via the link, in a non-co-planar arrangement. The invention furthermore relates to a method for producing tridecanal.