Engineering microporous ethane-trapping metal-organic frameworks for boosting ethane/ethylene separation

Realization of ethane-trapping materials for separating ethane (C₂H₆) from ethylene (C₂H₄) by adsorption, to potentially replace the energy-intensive cryogenic distillation technology, is of prime importance in the petrochemical industry. It is still very challenging to target C₂H₆-selective adsorbents with both high C₂H₆ capture capacity and gas selectivity. Herein, we report that a crystal engineering or reticular chemistry strategy enables the control of pore size and functionality in a family of isomorphic metal-organic frameworks (MOFs) for boosting the C₂H₆ uptake and selectivity simultaneously. By altering the carboxylic acid linker in Ni(bdc)(ted)_0.5, we developed two novel isoreticular MOFs, Ni(ndc)(ted)_0.5 and Ni(adc)(ted)_0.5 (termed ZJU-120 and ZJU-121, respectively), in which the pore sizes and nonpolar aromatic rings can be finely engineered. We discover that activated ZJU-120a with the optimized pore size (4.4 Å) and aromatic rings exhibits both a very high C₂H₆ uptake (96 cm³ g^-1 at 0.5 bar and 296 K) and C₂H₆/C₂H₄ selectivity (2.74), outperforming most of the C₂H₆-selective MOFs reported. Computational studies indicate that the suitable pore size and more nonpolar aromatic rings on the pore surfaces of ZJU-120a mainly contribute to its exceptional C₂H₆ uptake and selectivity. The breakthrough experiments demonstrate that ZJU-120a can efficiently separate C₂H₆ from 50/50 and 10/90C₂H₆/C₂H₄ mixtures under ambient conditions.