Multivariate Metal-Organic Frameworks Prepared by Simultaneous Metal/Ligand Exchange for Enhanced C2-C3 Selective Recovery from Natural Gas.

Recovering light alkanes from natural gas is a critical but challenging process in petrochemical production. Herein, we propose a postmodification strategy via simultaneous metal/ligand exchange to prepare multivariate metal-organic frameworks with enhanced capacity and selectivity of ethane (C 2 H 6 ) and propane (C 3 H 8 ) for their recovery from natural gas with methane (CH 4 ) as the primary component. By utilizing the Kuratowski-type secondary building unit of CFA-1 as a scaffold, namely, {Zn 5 (OAc) 4 } 6+ , the Zn 2+ metal ions and OAc - ligands were simultaneously exchanged by other transition metal ions and halogen ligands under mild conditions. Inspiringly, this postmodification treatment can give rise to improved capacity for C 2 H 6 and C 3 H 8 without a noticeable increase in CH 4 uptake, and consequently, it resulted in significantly enhanced selectivity toward C 2 H 6 /CH 4 and C 3 H 8 /CH 4 . In particular, by adjusting the species and amount of the modulator, the optimal sample CFA-1-NiCl 2 -2.3 demonstrated the maximum capacities of C 2 H 6 (5.00 mmol/g) and C 3 H 8 (8.59 mmol/g), increased by 29 and 32% compared to that of CFA-1. Moreover, this compound exhibited excellent separation performance toward C 2 H 6 /CH 4 and C 3 H 8 /CH 4 , with high uptake ratios of 6.9 and 11.9 at 298 K and 1 bar, respectively, superior to the performance of a majority of the reported MOFs. Molecular simulations were applied to unravel the improved separation mechanism of CFA-1-NiCl 2 -2.3 toward C 2 H 6 /CH 4 and C 3 H 8 /CH 4 . Furthermore, remarkable thermal/chemical robustness, moderate isosteric heat, and fully reproducible breakthrough experiments were confirmed on CFA-1-NiCl 2 -2.3, indicating its great potential for light alkane recovery from natural gas.