Bimetallic ions regulate pore size and chemistry of zeolites for selective adsorption of ethylene from ethane

Abstract

The petrochemical industry currently accomplishes olefin/paraffin separation by energy-intensive cryogenic distillation at an enormous scale. We report a sequential Ca2+/Ag+ ion-exchanged zeolite that achieves nearly ideal molecular sieving of C2H4/C2H6 and superior C2H4 adsorption capacity. Sequential and partial ion exchange regulates the pore size in ±0.2 Å increments, ranging between 3.8 and 4.2 Å. The demonstrated C2H4 adsorption capacity of 3.7 mmol/g, under ambient conditions, is the highest among zeolite-based materials. Elaborated with DFT calculations, Ag+-induced the stretching of the C-H bond and reduction of H-C-H bond angle of the C2H4 molecule in confined pore, providing C2H4 with the molecular basis and favorable kinetics for selective admission to pore size even less than 4 Å. The strategy of using bimetallic ions to regulate pore aperture size and selective admission of gas molecules with favorable kinetics provides a general path to be extended to other analogous molecular separation processes.