Bromine functionalization of metal–organic frameworks to improve ethane/ethylene separation

Abstract

Metal–organic frameworks (MOFs) have undergone extensive study as ethane-selective adsorbents for ethane/ethylene (C2H6/C2H4) separation, a process currently conducted through energy-intensive cryogenic distillation in the petrochemical industry. Herein, we present the effect of functionalization using bromine, known for its high polarizability, on the C2H6-selective adsorption properties of MOF. This approach, based on the slightly larger polarizability of C2H6 compared to C2H4, was systematically investigated using three isostructural MOFs: DMOF-1, DMOF-1-Br, and DMOF-1-Br2, featuring 1,4-benzenedicarboxylate, 2-bromo-1,4-benzenedicarboxylate, and 2,5-dibromo-1,4-benzenedicarboxylate ligands, respectively. While their C2H6/C2H4 selectivity, based on the ideal adsorbed solution theory, increased (from 1.51 to 1.75 at 298 K and 100 kPa for the 1/1 (v/v) mixture) with the rising Br content, breakthrough experiments revealed that DMOF-1-Br achieves the highest high-purity (>99.95 %) C2H4 productivity (9.7 LSTP kg−1 at 298 K and 100 kPa for the 1/1 mixture and 22.2 LSTP kg−1 for the 1/15 mixture). This accomplishment is attributed to the appropriate bromine functionalization. Further insight into their C2H6-selective adsorption behavior was gained through canonical Monte Carlo and dispersion-corrected density functional theory simulations.