(449cq) Microscopic Study of Acid Gas Transport in Zeolitic Imidazolate Frameworks By Diffusion NMR

Zeolitic imidazolate frameworks (ZIFs) are a subset of metals organic frameworks and exhibit high micropore volume and surface area as well as exceptional thermal and chemical stabilities. These properties have made ZIFs an attractive candidate for a wide range of energy efficient industrial separations. One such application deals with the removal hydrogen sulfide (H₂S) and carbon dioxide (CO₂) from methane (CH₄) in natural gas streams. To successfully use ZIFs in such a separations, fundamental knowledge of microscopic diffusion of H₂S, CO₂ and CH₄ inside pore networks of ZIFs is essential. Furthermore, understanding of possible changes in transport properties of ZIFs caused by exposure to H₂S is also needed to characterize their potential in H₂S separations. In this study we use pulsed-field gradient nuclear magnetic resonance (PFG NMR) to measure microscopic diffusion of H₂S and CO₂ in a variety of ZIF types including ZIF-11, ZIF-8, ZIF-7, and ZIF-90.

The combination of high magnetic fields and large gradients in PFG NMR allows us to probe diffusion for displacements in the range of micrometers with great accuracy. As a result, it becomes possible to resolve intra- and inter-particle diffusion by studying diffusion behavior over a broad range of displacements and the corresponding diffusion times. The PFG NMR experimental data will be discussed in the context of the corresponding results of molecular simulations performed by the collaborators.