PURPOSE: To obtain carbon monoxide from a mixed gas containing carbon monoxide with a simple apparatus, by separating and concentrating carbon monoxide from the mixed gas using a packed layer consisting of activated carbon impregnated with cuprous halide and cuprous formate or acetate.

CONSTITUTION: Granular activated carbon is impregnated with cuprous halide and cuprous formate or acetate to obtain a packed layer of a carbon monoxide absorbent. A gas containing carbon monoxide is passed through the layer from one end at 50W200°C under pressure. The supply of the gas is stopped immediately before the passage of carbon monoxide through the layer, the layer is evacuated below the atmospheric pressure, and the generated carbon monoxide is collected. The above operations are repeated to separate carbon monoxide easily from a mixed gas.