Abstract: In a process for compressing a gas, associated with a unit (5) for separating a gas mixture, the compressor (1, 2, 7) comprises a number of stages less than that which would be necessary to produce an optimal compressor of the isothermal type compressing the same flow rate of the gas to the same pressure. The compressor may compress the gas mixture to be separated or a product of the separation.

Abstract: In this process having two turbines and at least two stages for compressing the cycle gas, the two turbines are fed at the same intake pressure, the cycle gas is expanded in the warm turbine down to a first exhaust pressure, and the cycle gas is expanded in the cold turbine down to a second exhaust pressure lower than the first exhaust pressure.

Abstract: Process and apparatus for the purification of hydrogen by cryogenic treatment of a gas containing also nitrogen oxides and unsaturated hydrocarbons as two types of constituents which react together in an undesirable fashion when cooling achieves an intermediate temperature higher than the low temperature of the treatment. The process comprises cooling the gas to a first temperature higher than that intermediate temperature; eliminating from the gas one of the two types of constituents at this first temperature; and continuing the cooling of the gas to the low temperature. The elimination of one type of component is effected by washing the gas with a liquid adapted to dissolve it. This liquid contains at least one saturated hydrocarbon and is obtained by a partial condensation of an auxiliary gas which contains at least one of hydrogen and a heavy constituent whose value can be increased.