Separation of Aromatics/Cyclic Aliphatics by Nonporous Adaptive Pillararene Crystals

The separation of cyclic aliphatics of high purity, which are produced from hydrogenation of the corresponding aromatics, is highly desired in the chemical industry. An energy-efficient and environmentally friendly adsorptive separation method using nonporous adaptive crystals of perethylated pillar[5]arene (EtP5) and pillar[6]arene (EtP6) is described. Adaptive EtP5 crystals separate toluene from methylcyclohexane with 98.8 % purity, while adaptive EtP6 crystals separate methylcyclohexane from toluene with 99.2 % purity. The selectivities come from the stability of new EtP5 and EtP6 crystal structures upon capture of toluene and methylcyclohexane, respectively. The reversible transformations between nonporous guest-free EtP5 or EtP6 structures and guest-loaded structures make them highly recyclable.