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 (C 3 H 6 /C 3 H 8 ) and ethylene/ethane (C 2 H 4 /C 2 H 6 ) 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 2+, Co 2+ ), 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 2 ) decorated with high density of electronegative anions matches well with the cross section of C 3 H 6 (4.16 × 4.65 Å 2 ) and C 2 H 4 (3.28 × 4.18 Å 2 ), leading to efficient separation of C 3 H 6 /C 3 H 8 and C 2 H 4 /C 2 H 6 . 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 C 3 H 6 and 1.08 mmol g –1 C 2 H 4 from C 3 H 6 /C 3 H 8 and C 2 H 4 /C 2 H 6 mixtures, respectively. The separation selectivity for C 3 H 6 /C 3 H 8 on ZU-36-Ni calculated from the breakthrough tests is 19, which sets a new benchmark for C 3 H 6 /C 3 H 8 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.