Robust Metal–Organic Frameworks with High Industrial Applicability in Efficient Recovery of C3H8 and C2H6 from Natural Gas Upgrading

Developing efficient adsorbents with high uptake and selectivity for separation and recovery of C2H6 and C3H8 from natural gas is an important but challenging task. In this work, we demonstrate that high surface polarity and suitable pore diameter are two key factors that can synergistically enhance the separation performance, exemplified by metal–organic framework (MOF)-303 and MIL-160 (MIL: Matériaux de l’Institut Lavoisier), both possessing one-dimensional (1D) open channels with high density of heteroatoms and desired pore size (5∼7 Å). Significantly, the uptake of MOF-303 for C3H8 is up to 3.38 mmol g−1 at 298 K and 5 kPa with a record-high C3H8/CH4 (5:85, v/v) ideal adsorbed solution theory (IAST) selectivity of 5114 among all reported MOFs. In addition, MOF-303 also displays high C2H6 uptake capacity (at 10 kPa) and C2H6/CH4 (10:85, v/v) selectivity, reaching 1.59 mmol g−1 and 26, respectively. Owing to the larger pore diameter and lower density of heteroatoms within its 1D channels, MIL-160 shows apparently lower uptake and selectivity compared to those of MOF-303, though the values exceed those of majority of reported MOFs. Density functional theory (DFT) calculations verify that the high surface polarity and the suitable pore diameter synergistically enhance the affinity of the frameworks toward C3H8 and C2H6, giving rise to the high loading capacity and selectivity for C3H8 and C2H6. Both MOFs feature remarkable moisture stability without structural change upon exposure to 95% relative humidity (RH) for a month. In addition, synthesis of both compounds can be readily scaled up through one-pot reactions to afford about 5 g samples with high crystallinity. Finally, the substantial potential of MOF-303 and MIL-160 as advanced adsorbents for efficient separation of C3H8/C2H6/CH4 has been demonstrated by ternary breakthrough experiments, regeneration tests, and cyclic evaluation. The excellent separation performance, high stability, low cost, and good scalability endow both MOFs promising adsorbents for natural gas purification and recovery of C2H6 and C3H8.