Method for the separation of a hydrocarbon-rich, nitrogen-containing feed fraction (1, 101), preferably natural gas, a) wherein the feed fraction (1, 101) is at least in part liquefied (E1, E2) and divided by rectification into a nitrogen-enriched fraction (7, 14, 110) and a hydrocarbon-rich, nitrogen-depleted fraction (11, 111) and b) wherein, in the upper region of the rectification, a nitrogen-enriched stream is taken off, cooled and applied at least in part to the rectification as reflux and/or c) the nitrogen-enriched fraction is cooled and partially condensed, applied at least in part to the rectification as reflux and the remaining stream of the nitrogen-enriched fraction is subjected to a double-column process, wherein d) in the middle region of the rectification, a carbon-dioxide-poor stream (13, 113) which serves for cooling the nitrogen-enriched substream and/or cooling the nitrogen-enriched fraction is taken off, e) the feed fraction is rectified in a separation column having a dividing wall, wherein the dividing wall is arranged at least in the region of the separation column in which the feed fraction (2, 4, 5, 102, 104, 105) is fed to the separation column and the carbon-dioxide-poor stream (13, 113) is taken off, and the feed fraction and the carbon-dioxide-poor stream are fed in and taken off on opposite sides of the dividing wall, and f) the carbon-dioxide-poor stream (13, 113) is expanded upstream of the heat exchange with the nitrogen-enriched stream that is to be cooled and/or upstream of the heat exchange with the nitrogen-enriched fraction that is to be cooled, is at least partly evaporated in the heat exchanger, on completion of heat exchange is fed to the heat exchanger and heated therein, then compressed to at least the pressure prevailing in the rectification, is cooled in the downstream heat exchanger, is liquefied and subcooled in the heat exchanger and is fed back (17, 124) to the rectification above the withdrawal point thereof on the side of the dividing wall on which it is taken off. a) wherein the feed fraction (1, 101) is at least in part liquefied (E1, E2) and divided by rectification into a nitrogen-enriched fraction (7, 14, 110) and a hydrocarbon-rich, nitrogen-depleted fraction (11, 111) and b) wherein, in the upper region of the rectification, a nitrogen-enriched stream is taken off, cooled and applied at least in part to the rectification as reflux and/or c) the nitrogen-enriched fraction is cooled and partially condensed, applied at least in part to the rectification as reflux and the remaining stream of the nitrogen-enriched fraction is subjected to a double-column process, d) in the middle region of the rectification, a carbon-dioxide-poor stream (13, 113) which serves for cooling the nitrogen-enriched substream and/or cooling the nitrogen-enriched fraction is taken off, e) the feed fraction is rectified in a separation column having a dividing wall, wherein the dividing wall is arranged at least in the region of the separation column in which the feed fraction (2, 4, 5, 102, 104, 105) is fed to the separation column and the carbon-dioxide-poor stream (13, 113) is taken off, and the feed fraction and the carbon-dioxide-poor stream are fed in and taken off on opposite sides of the dividing wall, and f) the carbon-dioxide-poor stream (13, 113) is expanded upstream of the heat exchange with the nitrogen-enriched stream that is to be cooled and/or upstream of the heat exchange with the nitrogen-enriched fraction that is to be cooled,