Process for producing alcohols by homogeneously catalysed hydroformylation of olefins to aldehydes and subsequent hydrogenation thereof, comprising the steps of: a) providing one or more olefins, syngas and a catalyst system and also optionally a solvent; b) hydroformylating the olefin(s) in the presence of the syngas and of the catalyst system in one or more than one hydroformylation reactor to form at least aldehyde and also high boilers; c) withdrawing a liquid hydroformylation effluent comprising aldehyde, olefin, dissolved syngas, catalyst system and high boilers from the hydroformylation reactor; d) optionally devolatilizing the liquid hydroformylation effluent; e) separating the liquid hydroformylation effluent in a first membrane separation unit into a product stream and a reactor return stream, wherein the catalyst system partitions into the reactor return stream; f) returning the reactor return stream into the hydroformylation reactor; g) optionally devolatilizing the product stream; h) separating the product stream in a thermal separation unit into a gaseous head product comprising aldehyde and olefin and a liquid bottom product comprising aldehyde, high boilers and catalyst complex; i) separating the bottom product in a second membrane separation unit into a permeate and a retentate, wherein the catalyst system partitions into the retentate; wherein the improvement consists in k) operating the thermal separation unit such that 80% to 98% of the mass introduced into the thermal separation unit with the product stream re-emerges from the thermal separation unit as head product; 1) and subjecting at least some of the head product of the thermal separation unit and the permeate of the second membrane separation unit to conjoint or separate hydrogenation. a) providing one or more olefins, syngas and a catalyst system and also optionally a solvent; b) hydroformylating the olefin(s) in the presence of the syngas and of the catalyst system in one or more than one hydroformylation reactor to form at least aldehyde and also high boilers; c) withdrawing a liquid hydroformylation effluent comprising aldehyde, olefin, dissolved syngas, catalyst system and high boilers from the hydroformylation reactor; d) optionally devolatilizing the liquid hydroformylation effluent; e) separating the liquid hydroformylation effluent in a first membrane separation unit into a product stream and a reactor return stream, wherein the catalyst system partitions into the reactor return stream; f) returning the reactor return stream into the hydroformylation reactor; g) optionally devolatilizing the product stream; h) separating the product stream in a thermal separation unit into a gaseous head product comprising aldehyde and olefin and a liquid bottom product comprising aldehyde, high boilers and catalyst complex; i) separating the bottom product in a second membrane separation unit into a permeate and a retentate, wherein the catalyst system partitions into the retentate; k) operating the thermal separation unit such that 80% to 98% of the mass introduced into the thermal separation unit with the product stream re-emerges from the thermal separation unit as head product; 1) and subjecting at least some of the head product of the thermal separation unit and the permeate of the second membrane separation unit to conjoint or separate hydrogenation.