A polycatenated molecular cage-based propane trap for propylene purification with recorded selectivity.

The propane (C3H8)-selective adsorption technology is recognized as the promising energy-efficient way to directly afford high purity propylene (C3H6). Here, a novel strategy via cage construction, combining with multiple interaction and shape selectivity, was raised to achieve preferential C3H8 adsorption. We revealed that the polycatenated molecular cage within a microporous framework of [Ni(bpe)2(WO4)] (bpe = 1,2-bis(4-pyridyl)ethylene) shown preferential C3H8 adsorption behavior with recorded C3H8/C3H6 selectivity (1.62 to 2.75), as well as the high adsorption enthalpy around 42 kJ mol-1. The cage afforded dense electronegative binding sites, enabling the multiple Cδ--Hδ+…Cδ- interaction with C3H8 molecule and thus the higher affinity for C3H8 than C3H6. Additionally, the cage exhibited shape selectivity to oblate C3H8, and was unfavorable to C3H6 with relatively planar configuration as indicated by modeling studies. The high purity propylene (99.6 %) was directly obtained without the extra adsorption-desorption cycles through the column breakthrough experiment.