NOVELTY - In the recovery of carbon monoxide (CO) from a starting gas (1) containing CO, hydrogen (H2) and methane (CH4), by cooling to give a 2-phase mixture (2) of H2-rich gas phase and CO-rich liquid phase followed by cryogenic scrubbing (64) with liquid CH4, the scrubbing is carried out in a second heat exchanger (dephlegmator) (E4), in which the gas phase is passed upwards in countercurrent to liquid CH4. Heat of solution released in scrubbing is taken up by indirect heat exchange with a coolant (5).    USE - Especially for recovering carbon monoxide from a starting gas obtained from crude synthesis gas by drying and removing carbon dioxide.    ADVANTAGE - Combination of the scrubbing column and scrubbing column cooler functions as a dephlegmator provides a more effective and less expensive cryogenic methane scrubbing arrangement. The scrubbing agent is kept at an almost constat temperature during passage through the dephlegmator, so that the amount of scrubbing gent required (for a given level of performance) is reduced. The dimensions of the scrubbing and loaded scrubbing agent purification plants can be reduced. The amount of energy required for cryogenic gas separation is also reduced.    DETAILED DESCRIPTION - Recovery of carbon monoxide (CO) from a starting gas (1) containing CO, hydrogen (H2) and methane (CH4) involves cooling the starting gas with a process stream to be heated to give a 2-phase mixture (2) of H2-rich gas phase containing CO and CH4 and CO-rich liquid phase containing H2 and CH4, then subjecting at least the gas phase to cryogenic scrubbing (64) with liquid CH4. The novel features are that CH4 scrubbing is carried out in a second heat exchanger (dephlegmator) (E4), in which the gas phase is passed upwards in countercurrent to supercooled liquid CH4; and latent heat released in the dissolution of scrubbed materials from the gas phase in CH4 (heat of solution) is taken up by indirect heat exchange with a coolant (5) passed through the dephlegmator (preferably in countercurrent to the CH4 for scrubbing). An INDEPENDENT CLAIM is included for corresponding CO recovery apparatus, comprising a cryogenic methane scrubbing plant, lines for supplying the process streams to heat exchanger(s) for cooling and partially condensing the starting gas, a loaded scrubbing agent regeneration system and a compressor for increasing the CO pressure to the required produst pressure, the novel feature being that the methane scrubber includes the dephlegmator (E4), cooled by a coolant stream (5), in which the two-phase mixture (2) is contacted in countercurrent with downwardly flowing methane scrubbing agent (64).    DESCRIPTION OF DRAWING(S) - The figure shows a schematic diagram of one form of the carbon monoxide (CO) recovery apparatus.    Starting gas (1)    Two-phase stream (2)    Gas stream from dephlegmator, of crude hydrogen (H2) (3)    Connecting lines (4,6,14,15,21, 30,32,34-37,41,42, 61-63,66,96,100)    Coolant stream (5)    Gaseous CO phase (7)    Residual gas from dephlegmator (8)    Liquid phase from dephlegmator, of CO, H2 and methane (CH4) (10)    Partial streams of liquid phase (11,13)    Intermediate reservoir (12)    H2-rich head fraction from stripper (20)    Combined stream (22)    Residual gas from heat exchanger (23)    First and second partial streams from sump of stripper, of CO and CH4 (31,33)    Head product from separating column (40)    CO product (43)    CO streams (44,91,97)    Residual CO (45)    Sump product from separating column, mainly of CO (60)    Supercooled CH4 scrubbing agent (64)    CH4 recycling line (65)    Scrubbing agent streams (67,68)    Excess methane (not required for scrubbing) (69)    CO streams (90,91,97)    Turbine exhaust (92)    Part of exhaust, used for heating (93)    Gaseous CO reservoir (98)    Partial streams of cooled CO (99,101)    Liquid-gas mixture (102)    First and second sections of compressor in heat exchanger (C1,C2)    Phase separator (D2)    Heat exchangers (E1,E3)    Dephlegmator (E4)    Pump (P1)    Hydrogen stripping column (T2)    CO-CH4 separating column (T3)    Decompression turbine (X1)    Throttles (a - l)