Abstract
Facilitated transport membranes containing silver ions have attracted much attention thanks to their high performance in olefin/paraffin separation. However, the poor long-term stability of such membranes remains a drawback that must be overcome to enable their practical use. In this work, silver ions were incorporated as ion complexes in the Pebax (R) 2533 matrix to increase their stability as a function of time. Two complexing agents were evaluated: ammonia and 15-crown-5-ether. Membranes of Pebax (R) 2533/Ag(NH3)(2)OH and Pebax (R) 2533/[Ag(15-crown-5-ether)]BF4 maintained stable selectivity for more than thirty days of observation without compromising permeability. Although complexation decreases the performance of silver compared to free ions, it significantly increases the long-term performance in ethylene/ethane separation. the complexing agents weaken the intensity and strength of Ag+/ethylene-pi complexation, but prevent the reduction of Ag(I) to Ag(0). In long-term single gas permeation tests, the Pebax (R) 2533/Ag(NH3)(2)OH membrane showed selectivity in the range of 12.3 to 9 for 39 days, while the Pebax (R) 2533/[Ag(15crown-5-ether)]BF4 membrane showed selectivity around 9 for 30 days. Mixed gas permeation studies allowed to identify conditions to maintain the separation performance above the upper bound for more than 40 days, under continuous membranes exposure to mixed gases. Increased stability compared to membranes reported in the literature was achieved.