Optimization of a denitrogenation PROCESS a natural gas stream

A method of separating 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 steps: a) Introduction of the mixture gas to be treated into a first distillation column to create, at the column top, a first gaseous stream enriched in methane and a level lower than that of the head of said column other gaseous stream; b) Introduction of said further gaseous stream from step a) into a second distillation column at a level lower than that of the head of said second column to create, at the head of this column, a second rich gaseous stream methane, characterized in that the nitrogen content of said second gaseous stream is at least 1.5 times lower than the nitrogen content of the first gaseous stream and in that of 5 mol% to 30 mol% of the methane originally present in the gaseous mixture to be processed is included in the second gas stream (15 ').