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 (gamma-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 gamma-Al2O3), and consequently the Ag atoms in these sorbents are more capable of forming pi-complexation bonds with olefins. ESCA results indicate a transfer of electron density from Ag+ to the Lewis acid sites of alumina, hence weakens the pi-complexation bonds with olefins. (C) 2000 Elsevier Science Ltd. All rights reserved.