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

Abstract

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 13× has been used in the process. The VSA operates at 2 bara adsorption pressure and 0.1 bara regeneration pressure thus maintaining a PH/PL 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.