Stepwise Engineering the Pore Aperture of a Cage-like MOF for the Efficient Separation of Isomeric C4 Paraffins under Humid Conditions

The separation of isomeric C4 paraffins is an important task in the petrochemical industry, while current adsorbents undergo a trade-off relationship between selectivity and adsorption capacity. In this work, the pore aperture of a cage-like Zn-bzc (bzc=pyrazole-4-carboxylic acid) is tuned by the stepwise installation methyl groups on its narrow aperture to achieve both molecular-sieving separation and high n-C4H10 uptake. Notably, the resulting Zn-bzc-2CH(3) (bzc-2CH(3)=3,5-dimethylpyrazole-4-carboxylic acid) can sensitively capture n-C4H10 and exclude iso-C4H10, affording molecular-sieving for n-C4H10/iso-C4H10 separation and high n-C4H10 adsorption capacity (54.3 cm(3) g(-1)). Breakthrough tests prove n-C4H10/iso-C4H10 can be efficiently separated and high-purity iso-C4H10 (99.99 %) can be collected. Importantly, the hydrophobic microenvironment created by the introduced methyl groups greatly improves the stability of Zn-bzc and significantly eliminates the negative effect of water vapor on gas separation under humid conditions, indicating Zn-bzc-2CH(3) is a new benchmark adsorbent for n-C4H10/iso-C4H10 separation.

Automated summary

In this study, the pore aperture of Zn-bzc was tuned to achieve molecular-sieving separation of isomeric C4 paraffins. The introduction of methyl groups greatly improved the stability of Zn-bzc and eliminated the negative effect of water vapor on gas separation. Notably, Zn-bzc-2CH(3) showed high selectivity for n-C4H10 and maintained high adsorption capacity under humid conditions.