Reflux of demethenization columns

A process for the separation of the components of a gas mixture to be treated comprising methane, nitrogen and at least one hydrocarbon having at least two carbon atoms, or a mixture of these hydrocarbons, comprising the following stages:

• a) introducing the gas mixture to be treated into a first distillation column, thereby producing, in the column bottom, a first liquid stream enriched in hydrocarbon having at least two carbon atoms and, at the column top, a first gas stream enriched in methane;
• b) introducing the said first liquid stream enriched in hydrocarbon having at least two carbon atoms resulting from stage a) into a second distillation column, thereby producing, at the top of this column, a second gas stream rich in methane and, in the bottom of this column, a second liquid stream comprising at least 85 mol % of the hydrocarbons having at least two carbon atoms initially present in the mixture to be treated;
• wherein a portion of the second gas stream rich in methane resulting from stage b) at the outlet of the top of the second distillation column is compressed to a pressure at least greater by 1 bar than the pressure of said second distillation column and then condensed in order to be introduced, for one portion, into the upper part of the first distillation column and, for the other portion, into the upper part of the second distillation column in order to carry out the reflux of said distillation columns.