Insights into the thermodynamic–kinetic synergistic separation of propyne/propylene in anion pillared cage MOFs with entropy–enthalpy balanced adsorption sites

Abstract

Propyne/propylene (C₃H₄/C₃H₆) separation is an important industrial process yet challenged by the trade-off of selectivity and capacity due to the molecular similarity. Herein, record C₃H₄/C₃H₆ separation performance is achieved by fine tuning the pore structure in anion pillared MOFs. SIFSIX-Cu-TPA (ZNU-2-Si) displays a benchmark C₃H₄ capacity (106/188 cm³ g⁻¹ at 0.01/1 bar and 298 K), excellent C₃H₄/C₃H₆ IAST selectivity (14.6–19.3) and kinetic selectivity, and record high C₃H₄/C₃H₆ (10/90) separation potential (36.2 mol kg⁻¹). The practical C₃H₄/C₃H₆ separation performance is fully demonstrated by breakthroughs under various conditions. 37.8 and 52.9 mol kg⁻¹ of polymer grade C₃H₆ can be produced from 10/90 and 1/99 C₃H₄/C₃H₆ mixtures. 4.7 mol kg⁻¹ of >99% purity C₃H₄ can be recovered by a stepped desorption process. Based on the in situ single crystal analysis and DFT calculation, an unprecedented entropy–enthalpy balanced adsorption pathway is discovered. MD simulation further confirmed the thermodynamic–kinetic synergistic separation of C₃H₄/C₃H₆ in ZNU-2-Si.