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 force-field-based molecular simulations, we evaluate the performance of bulk all-silica 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. Monte Carlo simulations in the isobaric−isothermal Gibbs ensemble (GEMC) are used to probe the selective adsorption behavior for these mixtures. Molecular dynamics simulations in the canonical ensemble are carried out to examine the transport behavior at loadings obtained from the GEMC simulations. Our results show that bulk MFI and the nanosheets 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.