Significant energy and capital savings are possible by using membrane technologies for propylene/propane separation, which is currently performed on a large scale by energy-intensive distillation processes. Zeolitic imidazolate frameworks (ZIFs) have emerged as promising membrane materials with strong molecular sieving property for gas separations, particularly propylene/propane separation. However, the existing fabrication methods of ZIF membranes rely on solution-based synthesis that is difficult to scale up. Here, we developed a novel all-vapor-phase membrane processing method based on the combination of atomic layer deposition (ALD) and ligand vapor treatment, both of which are carried out in vapor phase. In this method, ALD is used to deposit zinc oxide inside the pores of an asymmetric alumina support, producing a nonselective and low-flux (or even impermeable) ZnO-alumina composite support. After vapor treatment of the support using 2-methylimidazole vapors, the ZnO is converted to ZIF-8, creating a selective membrane that is partly confined inside the support pores. This transformation from a nonselective and impermeable material to a selective membrane is named ligand-induced permselectivation (LIPS). ZIF membranes made by the all-vapor LIPS method exhibited high mixture separation factor for propylene over propane, high propylene flux and unprecedented performance under high feed pressure (&gt; 7 atm).

Zeolitic imidazolate framework membranes made by ligand-induced permselectivation for propylene/propane separation

2019 Spring National Meeting

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