Selective olefin separations using silver(I) and copper(I) ions

The olefin-selective complexation capability of silver(I) ion has been utilized in various gas separation systems, including argentation gas chromatography (GC) and facilitated transport membranes. However, the separation performance of these systems is often impaired when silver(I) ion is reduced to metallic silver upon exposure to hydrogen under elevated temperatures. Ionic liquids (ILs) possess a number of highly advantageous properties such as negligible vapor pressure, high thermal stability, and structural tunability. When silver(I) and copper(I) ions are dissolved in ILs, hydrogen-catalyzed reduction can be minimized while its olefin complexation capability is effectively maintained. Nevertheless, a fundamental understanding of the olefin separation mechanism and silver(I)/copper(I) ion stabilization in silver salt/IL mixtures is scarce. In this presentation, a chromatographic study of silver(I) ion and copper(I) stability in terms of silver salt/IL composition and experimental parameters such as temperature and carrier gas types will be discussed. We will highlight approaches that can be employed to coordinate ligands to silver(I) ions in an effort to modulate olefin retention through olefin-ligand and silver(I) ion-olefin interations. A three-phase chromatographic model developed by treating silver(I) ion as a pseudophase will be demonstrated to investigate analyte partitioning based on the optimized conditions. From the model, three discrete analyte partition coefficients between the carrier gas, IL solvent, and silver(I) ion pseudophase are determined, and their contribution to olefin separation is studied. Lastly, the model is used to investigate the decrease in olefin separation capability due to silver(I) ion reduction by monitoring changes in analyte partition coefficients. This presentation will provide a guide for developing selective and sustainable olefin separation systems utilizing silver(I) ion and copper(I)-containing ILs.