Crystalline thiacalixarene assembly for adsorption ability toward linear and branched C6 alkane vapor isomers†

Effective separation of linear and branched C6 alkanes is of importance in the improvement of the research octane number of gasoline during the isomerization of linear alkanes. However, developing a novel material for this separation remains a challenge. Activated crystals with a collapsed “channel-like sorption site” by assembling p-bromothiacalix[4]arene propyl ether molecules after removing cyclohexane (CyC6) molecules that act as templates are classified as a nonporous adaptive crystal. The activated crystals are capable of storing branched alkanes such as isohexane (2-C6), 3-methylpentane (3-C6), and 2,2- and 2,3-dimethylbutane (2,2- and 2,3-C6) vapors in the single-component system. In contrast, no sorption of n-hexane (n-C6) as one of the linear alkanes was observed. In these branched alkanes, the crystals preferentially adsorbed more branched alkanes, specifically 2,2-C6 and 2,3-C6, compared to mono-branched alkanes like 2-C6 and 3-C6 in two-component systems. Surprisingly, slight adsorption of n-C6 was observed in the system. The retention capacity of mono- and di-branched and linear alkanes in the crystals follows the order: 2,2-C6 ≈ 2,3-C6 > 3-C6 > 2-C6 ≫ n-C6.