Effect of impurities on ultra-pure hydrogen production by pressure vacuum swing adsorption

The most viable technology for production of ultra-pure hydrogen (>99.99%), required for fuel cells, is steam methane reforming (SMR) coupled with pressure vacuum swing adsorption (PVSA). A PVSA process with a two-layer bed of activated carbon (AC)/zeolite 5A for ultra-pure hydrogen production from syngas was developed and simulated with the aim of exploring the effect of impurities on energy intensity of the process. The simulated concentration profiles showed that CH₄ was removed by the first half of the AC layer, CO₂ and CO were mostly removed by the end of that layer, but zeolite 5A (the second layer) could not completely remove the remaining N₂. Further, the effect of the N₂ on performance of the PVSA process was demonstrated by simulating purification of two feeds with 3.1 and 1.1 vol% N₂, respectively. The 2% drop in N₂ concentration in the syngas feed resulted in decreased energy consumption of the PVSA process from 940 kJ/kg to 430 kJ/kg H₂, while H₂ recovery increased from 47% to 55%. Therefore, the presence of N₂ has a very large impact on recovery and energy intensity of the ultra-pure hydrogen production process, and development of adsorbents with better N₂ removal performance is required.