Spacial regulation of precise aperture in metal–organic frameworks towards ultrahigh-selective mixed matrix membranes for low-energy-consumption C3H6/C3H8 separation

Membrane technology based on metal–organic framework (MOF) with molecular sieving properties is a promising alternative to energy-intensive conventional distillation for C3H6/C3H8 separation. However, precisely regulating the aperture of MOF materials for industrial separation processes with low energy consumption remains a significant challenge. Herein, we introduce a post-synthetic defect exchange, using ortho-trifluoromethylbenzoic acid (o-TBA) in defective UiO-66, resulting in a mixed matrix membrane (MMM) with a C3H6/C3H8 ideal selectivity of ∼ 104 and C3H6 permeability of ∼ 293 Barrer, and exhibiting a C3H6/C3H8 selectivity ∼ 36 with C3H6 permeability of ∼ 188 Barrer for a C3H6/C3H8 (50:50) mixture. Computational simulations confirm impact of o-TBA-UiO on reducing pore sizes and providing moderate propylene affinity. Static adsorption and solution-diffusion experimental results show that the o-TBA-UiO/6FDA-DAM membrane provides fast C3H6 diffusion rates but retards C3H8 diffusion, leading to ultrahigh C3H6/C3H8 selectivity. A large-area membrane of 2400 cm2 was prepared to promote practical applications, mainly because of the considerably enhanced affinity between o-TBA-UiO and 6FDA-DAM. At a feed pressure of 1 bar, the 1812-type membrane module exhibited a modest decline in single gas separation performance with a C3H6 permeability of ∼ 175 Barrer and a C3H6/C3H8 ideal selectivity of ∼ 96. Finally, a potential two-stage membrane process with low energy consumption was designed. This study provides a robust design for MOF-based MMMs with molecular sieving for energy-efficient gas separation.