Efficient Separation of Propene and Propane Using Anion-Pillared Metal-Organic Frameworks

Propylene/propane (C3H6/C3H8) separation is a momentous and challenging process for the production of polymer-grade C3H6 with high energy penalty. Here, we report the separation of C3H6 and C3H8 with two isostructural anion-pillared metal-organic frameworks [GeFSIX-2-Cu-i (also termed as ZU-32) and SIFSIX-2-Cu-i]. Interestingly, GeFSIX-2-Cu-i shows a high uptake ratio of C3H6/C3H8 (1.49 at 298 K and 1.0 bar), outperforming most of the existing materials, such as MOF-74 series (1.16-1.31), MAF-23-O (1.17), and CuBTC (1.12). Furthermore, the breakthrough experiments for C3H6/C3H8 (50/50, v/v) binary mixtures were performed on GeFSIX-2-Cu-i and SIFSIX-2-Cu-i, respectively. Under dynamic conditions, both GeFSIX-2-Cu-i and SIFSIX-2-Cu-i present excellent separation performance, especially for GeFSIX-2-Cu-i with a C3H6 capacity of 2.2 mmol g(-1) (calculated from breakthrough curves). The binding sites of GeFSIX-2-Cu-i for C3H6 and C3H8 were investigated by the first-principles density functional theory calculations, and the results reveal that the strong hydrogen-bonding interactions between GeF62- anions and C3H6 as well as pi - pi interactions between organic linkers and C3H6 lead to high C3H6 uptake on GeFSIX-2-Cu-i. This work indicates that the anion-pillared metal organic frameworks, with high hydrothermal stability, can be considered as candidates for the separation of C3H6/C3H8 mixtures.