Ultramicroporous Lonsdaleite Topology MOF with High Propane Uptake and Propane/Methane Selectivity for Propane Capture from Simulated Natural Gas

Propane (C3H8) is a widely used fuel gas. Metal-organic framework (MOF) physisorbents that are C3H8 selective offer the potential to significantly reduce the energy footprint for capturing C3H8 from natural gas, where C3H8 is typically present as a minor component. Here we report the C3H8 recovery performance of a previously unreported lonsdaleite, lon, topology MOF, a chiral metal-organic material, [Ni(S-IEDC)(bipy)(SCN)]n, CMOM-7. CMOM-7 was prepared from three low-cost precursors: Ni(SCN)2, S-indoline-2-carboxylic acid (S-IDECH), and 4,4'-bipyridine (bipy), and its structure was determined by single crystal X-ray crystallography. Pure gas adsorption isotherms revealed that CMOM-7 exhibited high C3H8 uptake (2.71 mmol g-1) at 0.05 bar, an indication of a higher affinity for C3H8 than both C2H6 and CH4. Dynamic column breakthrough experiments afforded high purity C3H8 capture from a gas mixture comprising C3H8/C2H6/CH4 (v/v/v = 5/10/85). Despite the dilute C3H8 stream, CMOM-7 registered a high dynamic uptake of C3H8 and a breakthrough time difference between C3H8 and C2H6 of 79.5 min g-1, superior to those of previous MOF physisorbents studied under the same flow rate. Analysis of crystallographic data and Grand Canonical Monte Carlo simulations provides insight into the two C3H8 binding sites in CMOM-7, both of which are driven by C-H···π and hydrogen bonding interactions.