Pore control of Al-based MIL-53 isomorphs for the preferential capture of ethane in an ethane/ethylene mixture

Preferential ethane adsorption from an ethane (C2H6)/ethylene (C2H4) mixture has emerged as a promising alternative to energy-intensive cryogenic distillation for obtaining high-purity ethylene. In this study, MIL-53(Al) isomorphs were prepared using various organic linkers such as 1,4-benezenedicarboxylic acid (MIL-53-BDC), 2,6-naphthalenedicarboxylic acid (MIL-53-NDCA), and 4,4′-biphenyldicarboxylic acid (MIL-53-BPDC) to investigate their C2H6/C2H4 separation properties. C2H6/C2H4 separation performances were rigorously investigated by combining single-component gas adsorption, ideal adsorbed solution theory calculations, breakthrough experiments, and molecular simulations (Monte Carlo simulation and density functional theory calculations). All MIL-53 isomorphs exhibited preferential uptake of C2H6 in the C2H6/C2H4 mixture, among which MIL-53-NDCA exhibited a reasonably good C2H6/C2H4 selectivity (1.53) and the largest C2H6 uptake (4.24 mmol g−1) at 298 K and 1 bar. Molecular simulations revealed that the good C2H6/C2H4 separation performance can be attributed to efficient C–H⋯π interactions between C2H6 and the NDCA linker (Site I) and suppressed olefinic π⋯OH interactions between C2H4 and μ2-OH groups (Site II). In the breakthrough experiment using MIL-53-NDCA, a binary mixture of C2H6/C2H4 (50/50 v/v) was separated into high-purity ethylene (>99.95%) with ethylene productivity of 11.2 LSTP kg−1 at 298 K.