Flexible molecular sieving of C2H2 from CO2 by a new cost-effective metal organic framework with intrinsic hydrogen bonds

Abstract

The separation of C2H2/CO2 is an important process in industry but challenged by the trade-off of capacity and selectivity owning to their close physical properties and identical kinetic molecular size. Herein, we reported a new metal organic framework ZNU-3 (ZNU = Zhejiang Normal University) with flexibility controlled by abundant hydrogen-bonds for highly selective molecular sieving of C2H2 from CO2, CH4, C2H4 and C2H6 using commercially available cost-effective ligands. At 1.0 bar and 298 K, the uptake capacity of C2H2 is 81.0 cm3 (STP) g−1, while the CO2, C2H4, C2H6, CH4, N2 uptake capacities are only 5.4, 5.3, 1.0, 1.1, 1.1 cm3 (STP) g−1, respectively. Such high uptake ratios of C2H2 over other C2 and C1 gases have rarely been achieved. Particularly, the C2H2/CO2 uptake ratio of 14.9 is only secondary to that of the benchmark UTSA-300a and much higher than those of all other porous materials. Dynamic breakthrough experiments with equimolar C2H2/CO2 mixtures showed that the retaining time of C2H2 is nearly 2 fold of that of CO2, indicating the excellent practical separation performance of ZNU-3 for C2H2/CO2 mixtures. Modeling studies indicated that C2H2 is mainly trapped by two opposite carboxylic groups with additional small contribution from π···π packing between pyridine ring and planar C≡C moiety.