Separation of xylene isomers in an adaptable metal-organic framework.

Efficient separation of xylene isomers by adsorption remains challenging due to insufficient selectivity arising from their molecular similarity. We report an adaptable metal-organic framework, Ni(BIC)2 [1-H-benzimidazole-5-carboxylic acid (HBIC)], that exhibits high selectivity for para-xylene over other xylene isomers. Ni(BIC)2 features a guest-adaptive one-dimensional channel that precisely matches the molecular projection dimensions of para-xylene, enabling sieving from a quaternary mixture of xylene isomers. The structural transformation of Ni(BIC)2 upon guest adsorption substantially widens the disparity in binding energies between para-xylene and its counterparts. Weakly adsorbed components are converted into nonadsorbed entities, leading to temperature-independent para-xylene uptake while excluding meta-xylene and ortho-xylene. Breakthrough experiments demonstrate remarkable dynamic selectivity, delivering high-purity para-xylene within a single fixed-bed adsorption process. Simulated moving bed (SMB) process analysis demonstrates that Ni(BIC)2 delivers a 3.2-fold increase in production efficiency relative to conventional zeolite under milder operating conditions.