NOVELTY - There are means of sending a gas (23, 45) from the apparatus, probably part of the gas mixture to be separated, to a turbine (11) with bearings and means of sending at least part of the gas expanded in the turbine to a column in the system of columns when the expanded gas is part of the mixture to be separated. The turbine bearings are gas or rolling or magnetic bearings.    USE - Used for separating gas mixtures into their components, in particular air to obtain oxygen and nitrogen.    ADVANTAGE - The absence of lubrication on the various bearings prevents contamination of the separated gases by lubricant.    DETAILED DESCRIPTION - The apparatus includes a system of columns (13, 15); means of sending a gas to be separated (11) to a column in the system of columns; means of extracting at least one product (33, 35, 39, 41) from the system of columns and the turbine (11). The bearings are not oiled or lubricated. The gas to be separated contains oxygen and/or nitrogen and/or hydrogen and/or methane and/or carbon monoxide as its main components. The expanded gas is air, oxygen or hydrogen. The turbine is installed at least 1 meter below ground, preferably at least 2 meters below ground, or even 5 meters below ground. The turbine is braked by a suppressor brake (9), possibly of a centrifuge type, placed on the same axle as the turbine, all the bearings on this common axle are not lubricated. All the bearings on the common axle are gas bearings or all roller bearings. Alternatively, the turbine is braked by a generating brake with bearings which are not lubricated, in particular these bearings are magnetic.    An INDEPENDENT CLAIM is included for separating a gas mixture by cryogenic distillation in which the mixture to be separated is treated in an apparatus as above, and the generator brake is driven at the same speed as the turbine.    DESCRIPTION OF DRAWING(S) - The figure shows a cryogenic air distillation unit with an air cycle    Air flow (1)    Compressor (3)    Purification unit (5)    Heat exchanger (7)    Suppressor (9)    Turbine (11)    Medium pressure column (13)    Low pressure column (15)    Expanded gas (23)    Pure nitrogen (31)    Residual nitrogen (33)    Gaseous oxygen (35)    Liquid nitrogen (39)    Liquid oxygen (41)