Optimizing gate-opening pressure to boost propylene/propane separation by metal doping in isostructural MOFs

Abstract

Adsorption separation is one of the very advanced methods for C₃H₆ purification from C₃H₈ compared to energy-intensive cryogenic distillation, in which stimuli-responsive MOF adsorbents enable efficient separation via controlling differential gate-opening pressures for different gases. Herein, three designed isostructural M-odp (M = Co, Mg and Mn) MOFs showed interesting and distinct gate-opening pressures for C₃H₆ and C₃H₈ adsorption due to different structural flexibility. Furthermore, by means of an easily operated metal doping strategy, a family of MOFs with precisely regulated gate-opening pressures was fabricated. Upon employing the optimized trimetallic-doped Co_0.377Mg_0.597Mn_0.026-odp-a it was observed that the gate-opening pressure was reduced for C₃H₆ but elevated for C₃H₈, leading to the rare sieving separation for the two gases and achieving an exceptional C₃H₆/C₃H₈ selectivity of 84.4 (8.8× higher than that of monometallic Co-odp) and polymer-grade C₃H₆ (20.3 L kg⁻¹, ≥ 99.5% purity) at 298 K.