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-C 4 H 10 uptake. Notably, the resulting Zn-bzc-2CH 3 (bzc-2CH 3 =3,5-dimethylpyrazole-4-carboxylic acid) can sensitively capture n-C 4 H 10 and exclude iso-C 4 H 10 , affording molecular-sieving for n-C 4 H 10 /iso-C 4 H 10 separation and high n-C 4 H 10 adsorption capacity (54.3 cm 3  g -1 ). Breakthrough tests prove n-C 4 H 10 /iso-C 4 H 10 can be efficiently separated and high-purity iso-C 4 H 10 (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-C 4 H 10 /iso-C 4 H 10 separation.