At process for separating a synthesis gas stream into a hydrogen (H2) rich vapour stream and a liquid carbon dioxide (CO2) stream in a CO2 condensation plant comprising the steps of: (A) feeding a synthesis gas stream having a pressure in the range of 10 to 120 barg to a compression system of the CO2 condensation plant thereby increasing its pressure to 150 to 400 barg and cooling the resulting high pressure (HP) synthesis gas against an external coolant to remove at least part of the heat of compression; (B) cooling the HP synthesis gas stream to a temperature in the range of -15 to -55 DEG C by passing the HP synthesis gas stream through a heat exchanger system in heat exchange relationship with a plurality of refrigerant streams that are produced subsequently in the process; (C) passing the cooled HP synthesis gas stream formed in step (B) either directly or indirectly to a gas-liquid separator vessel that is operated at substantially the same pressure as the heat exchanger system and withdrawing a high pressure (HP) hydrogen rich vapour stream from the top of the separator vessel and a high pressure (HP) liquid CO2 stream from the bottom of the separator vessel; ; and (D) feeding the HP hydrogen rich vapour stream from step (C) to the turboexpansion system wherein the hydrogen rich vapour stream is subjected to isentropic expansion in each of the turboexpanders of the series such that hydrogen rich vapour streams are withdrawn from the turboexpanders of the series at reduced temperature and at successively reduced pressures and wherein isentropic expansion of the hydrogen rich vapour in each of the turboexpanders of the series generates motive power thereby driving a machine that is a component of the CO2 condensation plant and/or driving an alternator of an electric generator.