Nanocrystalline Ag-ZK-5 zeolite for selective CH4/N2 separation

Abstract

Decreasing crystal size and introducing more electronegative extraframework metal cations to small-pore zeolites provide clear-cut advantages for small gas adsorption and separations. Here, nanocrystalline (similar to 100 nm) silver-exchanged ZK-5 (Ag-ZK-5) has been prepared and studied as an adsorbent for CH4/N-2 separation. Nanocrystalline Ag-ZK-5 was found to show a CH4 uptake of 1.6 mmol g(-1) at 298 K and 1.0 bar and an IAST CH4/N-2 selectivity of 11.8 in vacuum-swing adsorption mode, which are the highest values ever reported for zeolitebased adsorbents for CH4/N-2 separation. This zeolite is also characterized by fast adsorption kinetics and excellent regenerability, revealing its high potential for practical applications. It appears that nanocrystalline Ag-ZK-5 may have a more homogenous Ag+ distribution than the microcrystalline one, providing the former zeolite with a better CH4/N-2 separation performance.