Fine-Tuning and Selective-Binding within an Anion-Functionalized Ultramicroporous Metal-Organic Framework for Efficient Olefin/Paraffin Separation.

Olefin/paraffin separation is one of the intrinsically challenging tasks, mainly realized through the energy-intensive cryogenic distillation techniques. Here, we report the efficient separation of both propylene/propane (C3H6/C3H8) and ethylene/ethane (C2H4/C2H6) mixtures for the first time by a cheap and customized anion-functionalized metal-organic framework, ZU-36 (also termed as GeFSIX-3-M, M = Ni2+, Co2+), through molecular recognition and cross-section matching mechanism. Specifically, the pore window size of the fine-tuned ZU-36-Ni (4.42 × 4.42 Å2) decorated with high density of electronegative anions matches well with the cross section of C3H6 (4.16 × 4.65 Å2) and C2H4 (3.28 × 4.18 Å2), leading to efficient separation of C3H6/C3H8 and C2H4/C2H6. The high uptake capacity and separation selectivity of ZU-36-Ni were confirmed by adsorption isotherms and breakthrough tests. Binary dynamic breakthrough results showed that ZU-36-Ni can trap 1.35 mmol g-1 C3H6 and 1.08 mmol g-1 C2H4 from C3H6/C3H8 and C2H4/C2H6 mixtures, respectively. The separation selectivity for C3H6/C3H8 on ZU-36-Ni calculated from the breakthrough tests is 19, which sets a new benchmark for C3H6/C3H8 separation. The proposed cross-section matching mechanism together with proper selective binding affinity may serve as a guide for the design of effective porous materials for other important gas separation.