Highly Selective, High-Capacity Separation of o-Xylene from C₈ Aromatics by a Switching Adsorbent Layered Material

Purification of the C₈ aromatics (xylenes and ethylbenzene) is particularly challenging because of their similar physical properties. It is also relevant because of their industrial utility. Physisorptive separation of C₈ aromatics has long been suggested as an energy efficient solution but no physisorbent has yet combined high selectivity (>5) with high adsorption capacity (>50 wt %). Now a counterintuitive approach to the adsorptive separation of o-xylene from other C₈ aromatics involves the study of a known nonporous layered material, [Co(bipy)₂(NCS)₂]_n (sql-1-Co-NCS), which can reversibly switch to C₈ aromatics loaded phases with different switching pressures and kinetics, manifesting benchmark o-xylene selectivity (S_OX/EB≈60) and high saturation capacity (>80 wt %). Structural insight into the observed selectivity and capacity is gained by analysis of the crystal structures of C₈ aromatics loaded phases.