Adaptive Throat-Sieving Gate in a Metal Azolate Framework Enabling Synergistic Equilibrium-Kinetic Separation of Propylene and Propane.

Abstract

Developing porous adsorbents for propylene/propane (C₃H₆/C₃H₈) separation faces the challenge of integrating high adsorption capacity with fast adsorption kinetics. Herein, we address this challenge through precise pore control in a slightly flexible metal azolate framework NUM-27a, enabling synergistic equilibrium-kinetic separation of C₃H₆/C₃H₈. The periodically expanded throat gate enables effective impeding the diffusion of C₃H₈, while a large pocket-shaped cavity decorated with exposed oxide groups facilitates exceptional C₃H₆ capture at low pressures. Specifically, NUM-27a achieves exceptional low-pressure C₃H₆ capture (89.61 cm³ cm^-3 at 0.1 bar) and a record C₃H₆ packing density (310.0 g L^-1 at 0.01 bar). Kinetic analysis further reveals effective diffusion coefficient for C₃H₆ is 1.57 × 10^-4 s^-1 at 298 K. Gas-loaded single crystal X-ray diffraction analysis coupled with computational simulations elucidate that the intrinsic pore geometry underpins the unique adsorption and separation performance. Breakthrough experiments validate the outstanding separation performance of NUM-27a for C₃H₆/C₃H₈ mixtures. Moreover, the great stability, recyclability, and low-cost precursors of NUM-27a underline its potential as a reliable adsorbent for C₃H₆/C₃H₈ separation. The work unveils the adaptive throat-sieving gate strategy with optimal separation performance for challenging gas separations.