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.