TECHNOLOGY FOCUS - POLYMERS - Preferred Method: At least one part of water vapor present in the starting stream and part of carbon dioxide present in the starting stream is separated from the starting stream to form water vapor and carbon dioxide containing permeate stream and hydrogen and carbon monoxide containing retentate stream in the first membrane step at 10-50 degrees C. At least one part of hydrogen and water vapor present in product stream of the Fischer-Tropsch reactor is separated at 75-250 degrees C to form hydrogen and water vapor containing permeate stream and hydrocarbon containing retentate stream in the second membrane step. At least one part of hydrogen in the gas phase of the first separator step is separated from light gases at 10-50 degrees C to form hydrogen containing permeate stream and light gases containing retentate stream in the third membrane step. The light gases containing retentate stream from the third membrane step is supplied to a fourth membrane step for the formation of light gases containing retentate stream and the permeate stream, which is concentrated to hydrocarbon having more than 2 carbon atoms. The light gases containing retentate stream of the fourth membrane step is mixed with the starting stream for recicrulation into the first membrane step. The permeate stream of the fourth membrane step is supplied to a fifth membrane step to form carbon dioxide containing permeate stream and hydrocarbon containing retentate stream of the fifth membrane step. At least one liquid fraction of the first separator step is supplied to a second separator step for separating at least one heavier fraction and a lighter fraction. The lighter fraction of the second separator step is mixed with the permeate stream of the fourth membrane step. Preferred Components: The membrane of the first membrane step comprises poly(ethylene oxide)terephthalate block copolymer membrane and/or polyether-polyamide block copolymer membrane. The membrane of the second membrane step comprises a polyimide membrane. The membrane of the third membrane step comprises a polyimide membrane. The membrane of the fourth membrane step comprises siloxane membrane. The membrane of the fifth membrane step comprises polyimide membrane.. EXAMPLE - No suitable example given.