(377f) Flexible MOFs for Gas Separation – a Case Study Based on Static and Dynamic Sorption Experiments

Porous metal organic frameworks (MOF’s) can be categorized into rigid and structurally flexible compounds. The latter change their structure influenced by external stimuli. Whether the corresponding phenomena such as gate opening or breathing could be utilized for gas separation applications, or not, is subject to ongoing research and controversial discussions.

In this work, two structurally flexible MOFs were selected for exploring guest-induced structural changes by adsorption of C4-hydrocarbons. Pure gas sorption isotherms of n-butane, isobutane, 1-butene and isobutene reveal a stepwise increase of the surface excess loading associated with gate opening. Based on these isotherms, dynamic sorption experiments with one- and two-component adsorptives have been carried out on a packed bed at different inlet concentrations suggested by the gate opening pressure determined in the isotherm measurements. This leads to stepwise breakthrough curves being affected by the entry concentrations. We discuss the chances and limitations originating from a flexible network transition on potential separation applications.

References

1. M. Lange, M. Kobalz, J. Bergmann, D. Lässig, J. Lincke, J. Möllmer, A. Möller, J. Hofmann, H. Krautscheid, R. Staudt and R. Gläser, Structural flexibility of a copper-based metal– organic framework: sorption of C4-hydrocarbons and in situ XRD, J. Mater. Chem. A, 2 (2014) 8075-8085
   2. Lange, M. Sorption of C4-hydrocarbons on structurally flexible, porous coordination polymers; University of Leipzig, Doctoral Thesis, 2015.
2. M. Kobalz, J. Lincke, K. Kobalz, O. Erhart, J. Bergmann, D. Lässig, M. Lange, J. Möllmer, R. Gläser, R. Staudt, H. Krautscheid, Paddle Wheel Based Triazolyl Isophthalate MOFs: Impact of Linker Modification on Crystal Structure and Gas Sorption Properties, Inorg. Chem., 55 (2016) 3030-3039

Acknowledgements
We gratefully acknowledge the synthesis of the materials and the scientific collaboration with Prof. Dr. Harald Krautscheidt and his group at the University of Leipzig.