Maximizing the Density of π-Electron in Metal-Organic Frameworks for Benchmark Paraffin Separation

Abstract

Selective paraffin adsorption is crucial in chemical processes but faces significant challenges. Herein a promising strategy by maximizing the density of π-electron (Dπ is defined to be Number(π-electron)/Volume(single pore)) of metal-organic framewok (MOF) pore is proposed to boost paraffin separation. SNNU-126 features a triangular prismatic pore with the highest Dπ value of 0.2070 e Å−3 is selected and rationally regulated by incorporating amino electron-donating groups (EDGs) to demonstrate the feasibility of this strategy. As expected, extraordinary Dπ value together with multiple EDGs endow SNNU-126-129 with top-level adsorption capacity, exceptional IAST selectivity, excellent separation ability as well as highest productivity. Specially, SNNU-129 with nine EDGs demonstrates the longest breakthrough interval times for C2H6/CH4 (205 min g−1) and C3H8/CH4 (710 min g−1) from the ternary gas mixture with one-step CH4 productivity of 15.56 mmol g−1 (purity > 99.5%) at 298 K and 1 bar, which surpass the values of all current adsorbents and set a benchmark for paraffin separation. In situ infrared spectra and DFT simulations clearly verify that maximizing the Dπ of MOF pore effectively enlarges the C─H···π interactions, widens the affinity gap, and results in extraordinary separation performance.