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

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 cm(3) (STP) g(-1), while the CO2, C2H4, C2H6, CH4, N-2 uptake capacities are only 5.4, 5.3, 1.0, 1.1, 1.1 cm(3) (STP) 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 pi center dot center dot center dot pi packing between pyridine ring and planar C C moiety.

Automated summary

The separation of C2H2/CO2 is crucial in industry, but the challenge lies in balancing capacity and selectivity due to their similar physical properties. This study introduces a new metal organic framework, ZNU-3, with controlled flexibility using abundant hydrogen-bonds, using cost-effective ligands for highly selective molecular sieving of C2H2 from CO2, CH4, C2H4, and C2H6.