High-purity nitrogen by pressure-swing adsorption

The separation of air for nitrogen production can be carried out by pressure-swing adsorption over a carbon molecular sieve. The separation is kinetically based since the equilibrium adsorption of both oxygen and nitrogen is very similar, but the oxygen is adsorbed faster. Several theoretical and experimental studies have been reported, but mainly dealing with nitrogen purities below 99.9%. The objective of this article is to study experimentally the effect of different process variables on the performance of a rate-induced PSA process in the high-purity region. The effect of cycle time on both the yield and the specific product per unit cycle become more significant as the purity increases. On the other hand, the specific feed per unit cycle is almost insensitive to product purity, particularly as the cycle time increases. These results agree very well with predictions from a theoretical model.