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Ammonia separation from N2 and H2 over LTA zeolitic imidazolate framework membranes
Journal of Membrane Science  (IF8.742),  Pub Date : 2021-01-14, DOI: 10.1016/j.memsci.2021.119078
Qiushi Wei, Jolie M. Lucero, James M. Crawford, J. Douglas Way, Colin A. Wolden, Moises A. Carreon

LTA type zeolitic imidazolate framework membranes denoted as ZIF-21 were synthesized and evaluated for the separation of a commodity chemical, ammonia, from nitrogen and hydrogen. Membranes were grown using secondary seeded growth. Ammonia permeances were as high as 1727 GPU, with NH3/N2, and NH3/H2 ideal selectivities of 35, and 12 respectively. ZIF-21 membranes were also evaluated for gas mixtures composed of 13.8:86.2 NH3/N2 and NH3/H2, with mixture separation selectivities as high as 7.6 for NH3/N2. Differences in adsorption, and diffusivities were identified as the key separation mechanisms. Specifically, for both gas pairs the polar-polar interaction between ammonia and the linker polar channels, led to the preferential adsorption of ammonia, and therefore favored thermodynamically the separation of ammonia from nitrogen and hydrogen. In addition, for NH3/N2 gas pair, differences in diffusivities was a contributing separation mechanism. For NH3/H2 gas pair, due to the faster hydrogen diffusivity, the kinetic contribution was a strong competing separation mechanism.