Separation of Linear and Branched Alkanes Using Host-Guest Complexation of Cyclic and Branched Alkane Vapors by Crystal State Pillar[6]arene

Activated crystals of pillar[6] arene produced by removing the solvent upon heating were able to take up branched and cyclic alkane vapors as a consequence of their gate-opening behavior. The uptake of branched and cyclic alkane vapors by the activated crystals of pillar[6] arene induced a crystal transformation to form one-dimensional channel structures. However, the activated crystals of pillar[6] arene hardly took up linear alkane vapors because the cavity size of pillar[6] arene is too large to form stable complexes with linear alkanes. This shape-selective uptake behavior of pillar[6] arene was further utilized for improving the research octane number of an alkane mixture of isooctane and n-heptane: interestingly, the research octane number was dramatically improved from a low research octane number (17%) to a high research octane number (> 99%) using the activated crystals of pillar[6] arene.