To reduce the dissipation of methanol from a CO2 vent of a synthesis gas apparatus in an ammonia plant or a hydrogen plant.

A condensate having been subjected to stripping which is to be circulated is brought into contact with a crude synthesis gas from a low temperature shift converter to absorb methanol therein. The synthesis gas is treated in a purifier to prepare a CO2 product with a reduced content of methanol which is to be diffused. The condensate from the contact step is subjected to stripping with steam to form a process steam stream suitable to be fed into a modifier and a process condensate stream having been stripping-treated suitable for polishing outside the facilities, and part of this condensate is circulated to be brought into contact with the synthesis crude gas.