Mixed (Ag+, Ca2+)-LTA zeolite with suitable pore feature for effective separation of C3H6/C3H8

Separating C3H6/C3H8 is a challenging task owing to their similar sizes and boiling points. In this study, we report a sequential and partial Ag+/Ca2+ ion-exchanged zeolite that exhibits ideal C3H6/C3H8 molecular sieving. Moreover, the zeolite exhibited superior C3H6 uptake of 2.37 mmol/g and molecular packing density (similar to 77% packing of liquid C3H6) at an extremely high C3H6: Ag(+ )ratio of 21.5 with Ag content as low as 1.18 wt%. The (Ag+, Ca2+) cations were sequentially exchanged into LTAs by comprehensively considering the extra-framework cation distribution and site preferences for different cations. By exchanging Ag+ with Na+ in the extra-framework of LTA, C3H6 can be admitted even at the average LTA apertures of sizes < 4 angstrom. Meanwhile, exchanged Ag+ also increased the adsorption kinetics of C3H6 by an order of magnitude. Hydrophobic modification on Ca-Ag-LTA was successfully achieved to significantly suppress the competition from water while retaining excellent regenerability in multiple cycles. The strategy of binary ion exchange to delicately tune the pore channels and chemistry and selectively admit molecules with beneficial kinetics might potentially be broadened to other industrial separation processes.