Pressure swing adsorption process for producing hydrogen and carbon dioxide

A pressure swing adsorption process (PSA) for recovery of H2 and CO2 from an input feed gas which contains at least 40% vol of H2, the pressure swing adsorption process comprising:

• a) feeding the input feed gas, which contains H2, CO2 and other components or impurities, through an adsorbent material suitable to adsorb CO2, in a pressure vessel under a high pressure, and withdrawing from the pressure vessel a first gas stream which is a H2-rich product gas containing less CO2 than the input feed gas due to adsorption of CO2 in the adsorbent material;
• b) lowering the pressure in the pressure vessel to a target intermediate pressure, which is lower than said high pressure, causing the adsorbent material to release a second gas stream, which is a gas containing impurities, H2 and CO2, and withdrawing said second gas from the pressure vessel;
• c) purging the adsorbent material by passing a CO2-rich purge stream through the adsorbent material, obtaining a third gas which is a purge gas containing impurities desorbed from the material, and withdrawing said third gas from the pressure vessel;
• d) lowering the pressure in the pressure vessel to a low pressure, which is lower than said intermediate pressure, and is a sub-atmospheric pressure, causing the adsorbent material to release under vacuum a fourth gas stream, which is a CO2-rich product gas containing CO2 desorbed from the material, and withdrawing said fourth gas from the pressure vessel;
• e) re-pressurizing the pressure vessel to said high pressure,
• wherein said steps a) to e) are performed cyclically in a pressure vessel or in a plurality of parallel pressure vessels of a multiple pressure vessel setup;
• wherein the sequence of steps performed by each pressure vessel includes an additional purge step which is performed after the step d) and before the step e), and said additional purge step is performed using part of the H2-rich product gas produced by the same or at least another pressure vessel, or said additional purge step is performed using a stream obtained from the blowdown step b) of at least another pressure vessel, and said additional purge step produces an additional CO2-rich product gas;
• wherein as a result of the above steps, CO2 and H2 contained in the input feed gas are recovered separately in the H2-rich product gas and in the CO2-rich product gas respectively, and impurities are removed in at least one further stream which is not recycled into the PSA process;
• and
• wherein at least part of said additional CO2-rich product gas is used to perform the step c) of at least one pressure vessel, and/or at least part of said additional CO2-rich product gas form part of the CO2 product.