Designing\nOpen Metal Sites in Metal–Organic\nFrameworks for Paraffin/Olefin Separations

Abstract

Incorporating open metal sites (OMS)\ninto metal–organic\nframeworks allows design of well-defined binding sites for selective\nmolecular adsorption, which has a profound impact on catalysis and\nseparations. We demonstrate that Cu­(I) sites incorporated into MFU-4<i>l</i> preferentially adsorb olefins over paraffins. Density\nfunctional theory (DFT) calculations show that the OMS are independent,\nwith no dependence of binding energy on olefin loading up to one olefin\nper Cu­(I). Experimentally, increasing Cu­(I) loading increased olefin\nuptake without affecting the binding energy, as predicted by DFT and\nconfirmed by temperature-programmed desorption. The potential of this\nmaterial for olefin/paraffin separation under ambient conditions was\ninvestigated by gas adsorption and column breakthrough experiments\nfor an equimolar ratio of olefin/paraffin. High-grade propylene and\nethylene (>99.999%) can be generated using temperature–concentration\nswing recycling from a Cu­(I)-MFU-4<i>l</i> packed column\nwith no measurable paraffin breakthrough.