according to the process of the invention , after heating , nitrogen which exits from a pressure column is compressed under elevated pressure by means of a single nitrogen compressor , and the low pressure column is operated at a pressure of about p n / ρ n , where p n represents the elevated pressure of nitrogen and ρ n the compression ratio of the nitrogen compressor . application to the simultaneous production on the one hand of high purity nitrogen at a pressure between 50 and 60 bars , and on the other hand , of oxygen at 65 bars , so as to supply a unit for the production of ammonia .