Functionalized and Hybridized ZIF-7 Adsorbents for Ethane-Ethylene Separation

The separation of light olefins from paraffins is considered as one of the separation processes with the potential to reshape the industrial world, owing to the current energy-intensive practice. Herein, we designed a series of functionalized and hybridized zeolitic imidazolate framework-7 (ZIF-7) adsorbents for ethane/ethylene separation based on pre- and post-synthesis functionalization, organic ligand modification, and hybridization with reduced graphene oxide (rGO). The gate opening mechanism, an intrinsic characteristic of ZIF-7 resulting from the rotation of the organic ligands, particularly benzimidazole, was explored to evaluate the effect of the applied modification strategies on the separation performance. The optimal adsorbent (ZIF-7-rGO-2), a ZIF-7 hybrid with rGO, exhibited a high equilibrium ethane capacity of 3.2 mmol/g at 298 K and 1 bar and an IAST ethane/ethylene selectivity of 4.5 for a 1/15 (v/v) mixture. Dynamic breakthrough experiments with a binary ethane/ethylene mixture (1/9, v/v) revealed cyclability by regeneration solely under inert gas flow at ambient conditions and a substantial time difference of 4.5 min between the elution time of the two gases thus resulting in a high breakthrough selectivity. The purity of the produced ethylene was >99.9%, and its productivity was 0.89 mmol/g, revealing that polymer-grade ethylene could be produced at ambient conditions from ethylene-rich gas stream. These findings provide valuable insights into the intricate dynamics of light olefin/paraffin separation and optimal ZIF-7 configurations, paving the way toward designing energy-efficient adsorption processes for this challenging separation.