Recovery of hydrogen and carbon dioxide from hydrogen PSA tail gas by vacuum swing adsorption

A five-step, two-column Vacuum Swing Adsorption (VSA) process has been demonstrated for hydrogen and carbon dioxide recovery from a simulated gas stream representing tail gas of polybed hydrogen PSA. An adsorber with a layered bed configuration consisting of commercial activated carbon and zeolite 13x has been used in the process. The VSA operates at 2 bar_a adsorption pressure and 0.1 bar_a regeneration pressure thus maintaining a P_H/P_L ratio of 20. By operating at shorter adsorption time, H₂ can be enriched from 25 mol% level in the tail gas to 99 mol% level at a recovery of around 80 mol%. At higher CO₂ loading of the bed obtained by operating at larger adsorption time, it is also possible to obtain sequestration grade CO₂ (> 95 mol% purity) with at least 90 mol% recovery from the evacuation step of the VSA. The average H₂ purity obtained in the latter scenario is ∼85 mol% level which can be recycled to the feed header of the main poly bed H₂ PSA after necessary compression. Recycling of recovered H₂ can lead to an increase in the overall productivity of the poly bed PSA unit for pure hydrogen production in a refinery. A possible location for the integration of the VSA process with the overall H₂ production scheme in a petroleum refinery and its impact in reducing CO₂ footprint for the H₂ production has been discussed.