Zeolitic Imidazolate Framework‑8 (ZIF-8) Membranes\nfor Kr/Xe Separation

Abstract

Herein, we demonstrate that a prototypical\ntype of metal organic\nframework, zeolitic imidazolate framework-8 (ZIF-8), in membrane form,\ncan effectively separate Kr/Xe gas mixtures at industrially relevant\ncompositions. The best membranes separated Kr/Xe mixtures with average\nKr permeances as high as 1.5 × 10^–8 ±\n0.2 mol/m² s Pa and average separation selectivities of\n14.2 ± 1.9 for molar feed compositions corresponding to Kr/Xe\nratio encountered typically in air. Molecular sieving, competitive\nadsorption, and differences in diffusivities were identified as the\nprevailing separation mechanisms. These membranes potentially represent\na less-energy-intensive alternative to cryogenic distillation, which\nis the benchmark technology used to separate this challenging gas\nmixture. To our best knowledge, this is the first example of any metal\norganic membrane composition displaying separation ability for Kr/Xe\ngas mixtures.