We present the simulation studies carried on separation of the N-2-O-2 mixture with the original and modified duplex PSA. The purities of products were in excess of 99 mol % with the modified duplex PSA, whereas the original duplex PSA yielded product purities of 72 mol %. For both product purities of 95 mol %, the bed size and energy requirements with the modified duplex PSA were less by 10 and 2.5 times respectively compared to the conventional PSA and were less by an order of magnitude compared to those with original duplex PSA.