Modification of a continuous zeolite membrane grown within porous polyethersulfone with Ag(I) cations for enhanced propylene/propane gas separation

Current commercial methods for propylene propane separation require energy intensive cryogenic distillation. Significant efforts are underway for alternative methods of separation, and include physical and chemical absorption and adsorption, as well as membrane separations. Polymer membranes have been the most extensively studied. Zeolites are mostly studied as adsorption supports, though there have been a few reports of zeolite membranes for propylene propane separation. The chemical bond between the double bond of olefins and Ag(I) and Cu(I) cations have been exploited in the chemically enhanced separation process for olefins and paraffins, using a variety of supports including polymers and zeolites. We have recently reported that continuous faujasitic membranes grown within an hour in porous polyethersulfone supports, and then covered with a thin layer of polydimethoxysilane can separate CO2 and N-2. In this study, we examine these membranes for propylene propane separation. The best separation results were obtained at 50 degrees C, with average propylene propane selectivity of 2.4 +/- 0.8, and propylene permeance of 1211 +/- 557 GPU. Membranes were also modified by ion-exchanging with two concentrations of Ag(I). Best results were obtained at 75 degrees C, with average propylene propane selectivity of 4.8 +/- 1.8, and propylene permeance of 1016 +/- 661 GPU. Comparison with the few studies that have used zeolite membranes indicate that the selectivity in these studies are higher by a factor of 2-3 as compared to the present study, though the permeance is higher in the present study, in some cases by several orders of magnitude.