Optimal Binding Affinity for Sieving Separation of Propylene from Propane in an Oxyfluoride Anion-Based Metal–Organic Framework

Abstract

Highly efficient adsorptive separation of propylene from propane offers an ideal alternative method to replace the energy-intensive cryogenic distillation technology. Molecular sieving-type separation via high-performance adsorbents is targeted for superior selectivity, but the limit in adsorption capacity remains a great challenge. Here, we report an oxyfluoride-based ultramicroporous metal–organic framework UTSA-400, [Ni(WO2F4)(pyz)2] (pyz = pyrazine), featuring one-dimensional pore channels that can accommodate the propylene molecules with optimal binding affinity while specifically excluding the propane molecules. The exposed oxide/fluoride pairs in UTSA-400 serve as strong functional sites for strengthened propylene–host interactions, accounting for a significantly enhanced propylene uptake, while the propane molecules are excluded due to the regulated host framework dynamics. The strong propylene binding enables near-saturation of propylene in the pore confinement at ambient conditions, leading to full utilization of pore space and superior packing density. Combined in situ infrared spectroscopy measurements and dispersion-corrected density functional theory calculations clearly unveil the nature of boosted host–guest binding. Direct production of polymer-grade (>99.5%) propylene with remarkable dynamic productivity is demonstrated by column breakthrough experiments. This work presents an example of pore engineering with atomic precision to break the trade-off in adsorptive separation through guest binding optimization.

A metal–organic framework based propylene nano-trap with dual functionalities for highly efficient propylene/propane separation

“…Evidently, ZJUT-2a, Co 2 ( m -dobdc), 25 UTSA-400 (ref. 14) and HIAM-301 (ref. 13) exhibit more balance between adsorption uptake and gas selectivity for C 3 H 6 /C 3 H 8 separation.…”

“…A number of MOFs have been developed in recent years to show high C 3 H 6 /C 3 H 8 separation performance based on equilibrium-based, kinetic-based, molecular sieving or gating-opening mechanisms. 12–30 Nevertheless, there commonly exists a trade-off challenge between uptake capacity and separation selectivity for most of the materials. For instance, several size-selective adsorbents with well-matched pore sizes ( e.g.…”

“…A number of MOFs have been developed in recent years to show high C 3 H 6 /C 3 H 8 separation performance based on equilibrium-based, kinetic-based, molecular sieving or gating-opening mechanisms. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Nevertheless, there commonly exists a trade-off challenge between uptake capacity and separation selectivity for most of the materials. For instance, several size-selective adsorbents with well-matched pore sizes (e.g., KAUST-7 and Co-gallate) enable complete size-exclusion of C 3 H 8 from C 3 H 6 to show record C 3 H 6 /C 3 H 8 selectivities but are commonly impaired by their relatively low gas uptakes.…”

A zirconium-based microporous metal–organic framework for molecular sieving CO2 separation

“…Metal–organic frameworks (MOFs), emerging as a class of advanced porous materials, have shown great potential as adsorbents for challenging gas separations owing to their diversity in composition, network topology, and feasible pore engineering. 4 To date, MOF adsorbents have shown great opportunities as CO 2 -selective adsorbents. One of the common strategies to develop MOFs for both pre-/post-combustion capture applications is to differentiate CO 2 from nitrogen and methane by manipulating the host–guest chemistry with CO 2 .…”

Rational design of metal–organic frameworks featuring macrocycle and helical chain motifs for propylene/propane separation

“…[10][11][12][13][14] The structural diversity, rich functionalities, and nely tuneable channels of MOFs make them promising candidates for C 3 H 6 /C 3 H 8 separation. [15][16][17][18][19][20] Kinetic separation relies on the varying transport rate of gas pairs into an adsorbent, which is particularly effective when separating molecules of similar sizes and polarities, as in the case of C 3 H 6 and C 3 H 8 . Kinetic separation features high energy efficiency compared to equilibrium separation, as the regeneration process is facilitated due to the absence of strong interactions, making it industrially advantageous.…”