Recovery of propylene from refinery off-gas using metal incorporated ethylcellulose membranes

Performance of certain modified ethylcellulose (EC) membranes was investigated for the recovery of propylene from a gas mixture, having the same composition as the absorber tail gas (ATG) of a fluid catalytic cracking unit of HPCL refinery, Vishakhapatnam. The mixture contains C1–C5 hydrocarbons and non-hydrocarbons such as CO, CO2, H2 and N2. Various metals such as silver, ruthenium, palladium and iridium were incorporated into EC membranes to modify the membrane permeation properties for selectively increasing the propylene flux by facilitating its transport. Ethylcellulose membranes appeared to have good potential for the commercial recovery of propylene from a hydrocarbon rich off-gas mixture containing the olefin as a major constituent. A reasonably high selectivity of 5.1 accompanied by high transport rates was obtained for propylene with respect to propane in the multicomponent mixture. Amongst the metal-incorporated membranes, the best results were obtained with a silver (5 wt.%)-EC membrane which yielded a permeate stream of around 65 mol% propylene. The permeation of the various other hydrocarbon components present in the ATG mixture through the metal incorporated EC membranes was also analyzed. Interaction of the metal ions with the membrane matrix has been explained by characterizing the films with the help of FTIR, WAXD and SEM–EDX techniques.