New Co-MOF adsorption material with pharynx-shaped channel and large cavity for record ethylene and propylene purification

Abstract

Ethylene (C₂H₄) and propylene (C₃H₆) produced by methanol to olefin (MTO) technology are important chemical raw materials. However, the purification and separation between C₂H₄ and C₃H₆ mixtures is very challenging. Herein, a novel microporous metal-organic framework (MOF) adsorbent Co₂(OATA)(DPA) was fabricated through mixed linkers of 5,5′-(oxalylbis(azanediyl))diisophthalic acid (H₄OATA) and V-shaped di(pyridin-4-yl)amine (DPA) with –NHCO– and –NH– functional groups, which was endowed with ideal small pore size, large cavity, and interesting C₃H₆ trap constructed by four sets of –NH– groups. Under 298 K and a crucial low pressure (0.05 bar) for the separation in microporous materials, the MOF shows ultra-high C₃H₆ preferential adsorption (97.8 cm³ g⁻¹) and considerable C₃H₆/C₂H₄ selectivity (about 22), representing an advanced material for the reported porous materials with C₃H₆/C₂H₄ separation function. The studies of single crystal X-ray diffraction and simulations showed that the customized pore limitation in the MOF provided stronger multiple attractive interactions with C₃H₆, leading to significant adsorption selectivity in the process of competing adsorption for C₃H₆ and C₂H₄. In one separation step, the MOF generated highly pure C₂H₄ (⩾99.9%) and C₃H₆ (⩾99.6%) products respectively from C₂H₄/C₃H₆ mixtures at different ratios, pressures, and temperatures.