NOVELTY - Separating a gas mixture comprising, e.g., hydrogen and methane, comprises, e.g., cooling gas mixture, during which condensate is deposited, supplying methane, ethane and/or ethylene-containing stream to distillation column, producing methane-, hydrogen and ethylene-containing-head product, and withdrawing as an overhead stream, depositing an ethyl-enriched liquid by cooling and supplying as reflux stream. At least a partial stream of portion of the gas mixture that remains in a gas state at second temperature level, is used for further cooling and the fluid of the partial stream is expanded.    USE - The method is useful for separating a gas mixture comprising hydrogen, methane, ethane and ethylene and optionally other hydrocarbons, using a distillation column (claimed).    ADVANTAGE - The method ensures minimized ethylene losses.    DETAILED DESCRIPTION - Separating a gas mixture comprising hydrogen, methane, ethane and ethylene and optionally other hydrocarbons, using a distillation column (122), comprises cooling the gas mixture from a first temperature level to a second temperature level which lies between the condensation temperatures of ethylene and methane, during which at least one condensate from the gas mixture is deposited, forming at least one methane, ethane and/or ethylene-containing stream from the condensate and at least partially supplying to the distillation column, producing methane- and hydrogen and further ethylene-containing-head product in the distillation column, and withdrawing as an overhead stream from the distillation column, depositing at least an ethyl-enriched liquid from the overhead stream by further cooling and supplying at least partially as reflux stream to the distillation column. At least a partial stream of portion of the gas mixture that remains in a gas state at the second temperature level, is used for further cooling of the overhead stream and the fluid of the partial stream is at least partially is expanded. INDEPENDENT CLAIMS are also included for:    (1) a separation unit for separating the gas mixture, comprising the distillation column, a device for cooling the gas mixture from a first temperature level to a second temperature level which lies between the condensation temperatures of ethylene and methane, and depositing at least a condensate from the gas mixture, a device for forming at least one methane, ethane and/or ethylene-containing stream from the condensate and at least partially supplying to the distillation column, a device for producing methane- and hydrogen and further ethylene-containing-head product in the distillation column and withdrawing as an overhead stream from the distillation column, a device for depositing at least an ethyl-enriched liquid from the overhead stream after further cooling and supplying at least partially as reflux stream to the distillation column, where the device utilizes at least a partial stream of portion of the gas mixture that remains in a gas state at the second temperature level, is used for further cooling of the overhead stream and the fluid of the partial stream is at least partially is expanded after using for cooling the overhead stream; and    (2) retrofitting the separation unit.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic representation of the separation unit.    Distillation column (122)    Liquid separator (131)    Pump (132)    Expansion turbine (135)    Heat exchanger (158)