Molecular Sieving of Ethane from Ethylene through the Molecular Cross-Section Size Differentiation in Gallate-based Metal-Organic Frameworks.

Purification of C2 H4 from an C2 H4 /C2 H6 mixture, one of the most important while challenging industrial separation processes, is mainly through energy-intensive cryogenic distillation. Now a family of gallate-based metal-organic framework (MOF) materials is presented, M-gallate (M=Ni, Mg, Co), featuring 3D interconnected zigzag channels, the aperture sizes of which (3.47-3.69 Å) are ideally suitable for molecular sieving of ethylene (3.28×4.18×4.84 Å3 ) and ethane (3.81×4.08×4.82 Å3 ) through molecular cross-section size differentiation. Co-gallate shows an unprecedented IAST selectivity of 52 for C2 H4 over C2 H6 with a C2 H4 uptake of 3.37 mmol g-1 at 298 K and 1 bar, outperforming the state-of-the-art MOF material NOTT-300. Direct breakthrough experiments with equimolar C2 H4 /C2 H6 mixtures confirmed that M-gallate is highly selective for ethylene. The adsorption structure and mechanism of ethylene in the M-gallate was further studied through neutron diffraction experiments.