(556g) Molecular Simulations Probing the Adsorption and Diffusion of Ammonia, Nitrogen, Hydrogen, and Their Mixtures in Bulk MFI Zeolite and MFI Nanosheets

Recent advances in the synthesis of MFI zeolite nanosheets have led to highly selective membranes that are promising candidates for small-scale ammonia separation from ammonia/nitrogen/hydrogen mixtures in distributed green ammonia
production plants. Using Monte Carlo and molecular dynamics simulations with interactions described either by transferable force fields or Kohn-Sham density functional theory, we evaluate the performance of bulk all-silica MFI zeolite, a hierarchical MFI zeolite, and MFI nanosheet and nanosheet stacks for ammonia/nitrogen/hydrogen separations over a wide range of state points including conditions relevant for a membrane-based reactor−separator process. Our results show that the hierarchical structure and nanosheets both with explicit surface silanols are highly selective toward ammonia adsorption, but
selectivity decreases with increasing temperature. Conversely, the diffusion selectivities toward ammonia are more favorable at process-relevant temperatures. Analysis of simulation trajectories provides insights on the higher selectivity observed for the nanosheets.

This research was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award DE-SC0023403. Computational resources, in part, were provided by the Minnesota Supercomputing Institute at the University of
Minnesota.