Mixed cation zeolites: Li(x)Ag(y)-X as a superior adsorbent for air separation

Li-X zeolite (Si/Al = 1.0) is currently the best sorbent for use in the separation of air by adsorption processes. Silver is also known to strongly affect the adsorptive properties of zeolites and thermal vacuum dehydration of silver zeolites leads to the formation of silver clusters within the zeolite. In this work we synthesized type X zeolites containing varying mixtures of Li and Ag. Adding very small amounts of Ag at the proper dehydration conditions formed silver clusters and enhanced adsorptive characteristics and energetic heterogeneity, as compared to those of the near fully exchanged Li⁺-zeolites. The performance for air separation by the best of these sorbents, containing, on average, only one Ag per unit cell, was compared to that of the near fully Li⁺-exchanged zeolite using a standard PSA cycle by numerical simulation. The results show that the new sorbent provides a significantly higher (> 10%) product throughput at the same product purity and recovery when compared to that of the near fully Li⁺- exchanged zeolite.