Jun-Xian Chen, Xian-Xian Xiao, Libo Li, Jinping Li, Rui-Biao Lin*, Xiao-Ming Chen*

Cite this article: Chin. J. Struct. Chem., 2025, 44(12), 100744. DOI: 10.1016/j.cjsc.2025.100744

Publication date: December 1, 2025

Keywords: Metal-organic frameworks; Isostructural; Gas separation; C₄ olefins; Pore tuning

ABSTRACT

Separation of ternary C4 olefins (n-butene, iso-butene and 1,3-butadiene) is very challenging but crucial in the petrol-chemical industry due to their similar molecular sizes and properties. Herein, to optimize the separation efficiency for separation of C4 olefins, a new Hofmann-type MOF, [Ni(piz)Ni(CN)4] (piz = piperazine)—isostructural to the typical one [Ni(pyz)Ni(CN)4] (pyz = pyrazine), has been synthesized by a facile method from aqueous solution. The pore size reduction of [Ni(piz)Ni(CN)4] (3.62 Å, in contrast to 3.85 Å in [Ni(pyz)Ni(CN)4]) results in negligible iso-butene (i-C4H8) uptake (from 2.92 to 0.04 mmol g−1) whereas retaining significant uptake for 1,3-butadiene (1,3-C4H6, 1.96 mmol g−1) and n-butene (n-C4H8, 1.47 mmol g−1), showing much higher uptake ratios of 1,3-C4H6/i-C4H8 (47) and n-C4H8/i-C4H8 (35) that outperform most of the benchmark porous materials for separating C4 olefins. Breakthrough experiments demonstrate successful separation of high-purity (99.9999%) i-C4H8 and 1,3-C4H6 from equimolar 1,3-C4H6/i-C4H8, n-C4H8/i-C4H8 and 1,3-C4H6/n-C4H8/i-C4H8 mixtures.