Metal ion modified PIM-1 and its application for propylene/propane separation

Polymers with intrinsic microporosity (PIMs) have attracted much attention from the membrane community due to the nature of high fractional free volume and high gas permeability. To explore their potential for C₃H₆/C₃H₈ separation, PIM-1 was hydrolyzed and incorporated with various metal ions such as Zn²⁺, Mg²⁺ and Ag⁺. Experimental results reveal that the pristine PIM-1 has poor C₃H₆/C₃H₈ separation. Analyses from positron annihilation lifetime spectroscopy suggest that hydrolyzed PIM-1 possesses a smaller free volume size and a less fractional free volume resulting in a higher C₃H₆/C₃H₈ selectivity of α=9.12 and a lower C₃H₆ permeability of 421 Barrer. The Ag⁺ ion treated membrane shows weak facilitated transport with a moderately improved C₃H₆ permeability of 759 Barrer and C₃H₆/C₃H₈ selectivity of 11.69. The Mg²⁺ ion treated membrane exhibits affinity to the π-orbital of olefin. It has a higher C₃H₆/C₃H₈ selectivity of 15.23 but a lower C₃H₆ permeability of 568 Barrer. The Zn²⁺ ion treated membrane displays the highest C₃H₆ permeability of 837 Barrer but a lower selectivity of 9.12. In addition, the results of pressure-dependent permeation tests indicates that the Zn²⁺ ion treated membrane has better plasticization resistance than other membranes.