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 (CH/CH) and ethylene/ethane (CH/CH) mixtures for the first time by a cheap and customized anion-functionalized metal-organic framework, ZU-36 (also termed as GeFSIX-3-M, M = Ni, Co), through molecular recognition and cross-section matching mechanism. Specifically, the pore window size of the fine-tuned ZU-36-Ni (4.42 × 4.42 Å) decorated with high density of electronegative anions matches well with the cross section of CH (4.16 × 4.65 Å) and CH (3.28 × 4.18 Å), leading to efficient separation of CH/CH and CH/CH. 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 CH and 1.08 mmol g CH from CH/CH and CH/CH mixtures, respectively. The separation selectivity for CH/CH on ZU-36-Ni calculated from the breakthrough tests is 19, which sets a new benchmark for CH/CH 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.