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.