Abstract: In a process for the separation of air by cryogenic distillation using a cryogenic distillation unit comprising at least a double column (1) including a high pressure column (2) and a low pressure column (3), in which air is compressed in a compressor (C) to a first pressure, cooled and purified air at the first pressure is compressed in first and second booster compressors (8, 11) to a second pressure and then cooled in a heat exchanger (5), at least part of the air at the second pressure is cooled and expanded in a first turbine (12) having a first inlet temperature, a first part of the air expanded in the first turbine is sent to the high pressure column and a second part of the air expanded in the first turbine is sent to the heat exchanger to be warmed, the warmed second part of the air is expanded in a second turbine (9), returned to the heat exchanger and further warmed and a portion of the air is compressed in the first booster compressor (8) to a pressure intermediate to the first and second pressure