PSA Processes for Production of Hydrogen Only

The most frequently used PSA process concept for sole production of hydrogen is patented by Union Carbide Corporation.9,10 One version of this process consists of nine cyclic steps 9 

A Poly-bed system consisting of 10 parallel columns, each containing a layer of activated carbon in the feed end and a layer of 5A zeolite in the product end, could process an SMROG (77.1% H2, 22.5% C02, 0.35% CO, and 0.013% CH4) at 20.7 atm and 21 °C to produce a 99.999% pure H2 product at near the feed gas pressure with a H2 recovery of 86.0%.9 The lowest desorption pressure (PD) for the process was 1 atm and the composition of the waste gas was 32.0% H2, 66.8% C02, 1.0% CO, and 0.04% CH4. The volume fractions of the carbon and the zeolite layers in the adsorbers were 0.762 and 0.238, respectively. The total cycle time (11 steps) used was 13.33min, and the feed processing capacity for the process was 34.9ft3 of feed gas (latm, 15°C/ft3) of total adsorbent in the system/cycle. 

A very interesting variation of the above-described process is patented by Toyo Engineering Corporation of Japan.12,13 The process is used for the recovery of H2 from a ROG. It consists of nine sequential steps  

Several other PSA process configurations have been proposed for purification and recovery of H2 from various ROG streams.15-19 

The A beds are packed with activated carbons that selectively remove C02 and H20 from the SMROG. The B beds are packed with zeolites for the selective removal of the remaining C02, CH4, CO, and N2 from H2. The process is designed in such a fashion that very little C02 breaks through the A beds during step (a). 

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