Water-Stable Microporous Bipyrazole-Based Framework for Efficient Separation of MTO Products

Recently, methanol-to-olefins (MTO) technology has been widely used. The development of new adsorbents to separate MTO products and obtain high-purity ethylene (C₂H₄) and propylene (C₃H₆) has become an urgent task. Herein, an exceptionally highly water-stable metal-organic framework (MOF), [Cu₃(OH)₂(Me₂BPZ)₂]·(solvent) (1) (H₂Me₂BPZ = 3,3'-dimethyl-1H,1'H-4,4'-bipyrazole) with hexagonal pores, has been elaborately designed and constructed. After being soaked in water for 7 days, it still maintains its structure, and the uptake of N₂ at 77 K is unchanged. The adsorption capacity of C₃H₆ can reach 138 cm³ g^-1, while the uptake of C₂H₄ is only 52 cm³ g^-1 at 298 K and 1 bar. The dynamic breakthrough experiments show that the mixture of C₃H₆/C₂H₄ (50/50, v/v) can be efficiently separated in one step. High-purity C₂H₄ and C₃H₆ can be obtained through an adsorption and desorption cycle and the yields of C₂H₄ (purity ≥ 99.95%) and C₃H₆ (purity ≥ 99%) are 84 and 48 L kg^-1, respectively. Surprisingly, when the flow rate is increased, the separation performance has no obvious change. Additionally, humidity has no effect on the separation performance. Finally, theoretical simulations indicate that there are stronger interactions between the C₃H₆ molecule and the framework, which are beneficial to capturing C₃H₆ over C₂H₄.