Abstract: Carbon monoxide is recovered by a cryogenic route from a gas mixture, for example from the tail gas of an operation for scrubbing with nitrogen in the preparation of an ammonia synthesis mixture, this mixture containing carbon monoxide, hydrogen and other constituents including nitrogen. The hydrogen is separated off by partial condensation and the other components by distillation of the condensate. The carbon monoxide is produced by distillation in two columns, of which only one has a head condenser fed with a flow of liquid carbon monoxide. A liquid flow is drawn at an intermediate level in the column with the head condenser and directed to the head of the other column.

Abstract: Carbon monoxide and hydrogen are from a gaseous mixture comprising essentially these two components and methane, by the steps of i) cooling the initial gaseous mixture so as partially to condense it; ii) separating a condensed portion of the mixture from an uncondensed portion containing principally hydrogen; iii) sending the condensed portion to a stripping column (7) to produce a gaseous fraction at the head of the column comprising hydrogen and a liquid fraction at the base of the column containing carbon monoxide and methane; iv) distilling the liquid fraction in a purification column (9) to produce substantially pure carbon monoxide at the head of the column and methane at the base of the column; and v) supplying a portion of the separation energy by a refrigeration cycle using an autonomous refrigeration fluid.