Efficient Separation of Dibranched Hexane from its Linear and Monobranched Isomers via the Synergistic Molecular Sieving and Pore Shape-Matching Strategy.

The efficient separation of dibranched hexane from its linear and monobranched isomers is crucial but challenging for the production of high-RON (Research Octane Number) gasoline. Here, a strategy is presented to realize the efficient separation of high-purity (99.8%) dibranched 2,2-dimethylbutane from a ternary mixture of n-hexane/3-methylpentane/2,2-dimethylbutane by combining the sieving aperture and shape-matching cavity within the ultramicroporous metal-organic framework, ZnO(NTB) (HNTB = 4,4',4″-Nitrilotrisbenzoic acid). The static adsorption isotherms exhibit both high capacity for linear n-hexane (2.72 mmol g) and monobranched 3-methylpentane (2.59 mmol g). Dynamic breakthrough experiment shows that ZnO(NTB) is capable of completely separating high-RON dibranched 2,2-dimethylbutane with a record-high productivity (0.98 mmol g), which is ≈1.6 times that of the previous benchmark material. Single-crystal X-ray diffraction of guest-loaded ZnO(NTB) reveals that there exist high-density elongated cavities that match well with the shape of both n-hexane and 3-methylpentane, which can account for the high adsorption capacity for both of them. This work demonstrates the effectiveness of the synergistic effect of molecular sieving and shape matching in the efficient production of dibranched hexane from complex mixture.