Functionalized\nand Hybridized ZIF‑7 Adsorbents\nfor Ethane-Ethylene Separation

The separation of light olefins from paraffins is considered\nas\none of the separation processes with the potential to reshape the\nindustrial world, owing to the current energy-intensive practice.\nHerein, we designed a series of functionalized and hybridized zeolitic\nimidazolate framework-7 (ZIF-7) adsorbents for ethane/ethylene separation\nbased on pre- and post-synthesis functionalization, organic ligand\nmodification, and hybridization with reduced graphene oxide (rGO).\nThe gate opening mechanism, an intrinsic characteristic of ZIF-7 resulting\nfrom the rotation of the organic ligands, particularly benzimidazole,\nwas explored to evaluate the effect of the applied modification strategies\non the separation performance. The optimal adsorbent (ZIF-7-rGO-2),\na ZIF-7 hybrid with rGO, exhibited a high equilibrium ethane capacity\nof 3.2 mmol/g at 298 K and 1 bar and an IAST ethane/ethylene selectivity\nof 4.5 for a 1/15 (<i>v/v</i>) mixture. Dynamic breakthrough\nexperiments with a binary ethane/ethylene mixture (1/9, <i>v/v</i>) revealed cyclability by regeneration solely under inert gas flow\nat ambient conditions and a substantial time difference of 4.5 min\nbetween the elution time of the two gases thus resulting in a high\nbreakthrough selectivity. The purity of the produced ethylene was\n>99.9%, and its productivity was 0.89 mmol/g, revealing that polymer-grade\nethylene could be produced at ambient conditions from ethylene-rich\ngas stream. These findings provide valuable insights into the intricate\ndynamics of light olefin/paraffin separation and optimal ZIF-7 configurations,\npaving the way toward designing energy-efficient adsorption processes\nfor this challenging separation.