New sorbents for olefin/paraffin separations by adsorption via π-complexation: Synthesis and effects of substrates

New adsorbents for olefin/paraffin separations are synthesized by effective dispersion of Ag⁺ cations on high-surface-area substrates. Two techniques for synthesis are compared: thermal monolayer dispersion and incipient wetness impregnation. The incipient wetness impregnation technique yields the best sorbents that show the highest selectivities, olefin capacities, reversibility and fast rates. AgNO₃ is dispersed on three substrates (γ-Al₂O₃, SiO₂ and MCM-41 mesoporous molecular sieve) via incipient wetness impregnation for ethane/ethylene and propane/propylene separations. The surface chemistry of the substrate plays an important role in olefin adsorption. The silica surface (on both silica gel and MCM-41) provides a better substrate due to its lack of Lewis acid sites (unlike γ-Al₂O₃), and consequently the Ag atoms in these sorbents are more capable of forming π-complexation bonds with olefins. ESCA results indicate a transfer of electron density from Ag⁺ to the Lewis acid sites of alumina, hence weakens the π-complexation bonds with olefins. (C) 2000 Elsevier Science Ltd. All rights reserved.