Olefin/Paraffin Separations by Adsorption: π-Complexation vs. Kinetic Separation

Monolayer dispersed AgNO₃ on silica gel was prepared by thermal dispersion. This sorbent exhibited superior adsorption properties for olefin/paraffin separations by selective adsorption of olefins through π-complexation. This sorbent, along with Ag⁺ ion-exchanged resin, was subjected to simulation studies for olefin/paraffin separations by pressure-swing adsorption. Kinetic separations (due to differences in olefin/paraffin diffusivities) using zeolite 4A and molecular-sieve carbon were also studied. Using 50/50 mixtures of C₂H₄/C₂H₆ and C₃H₆/C₃H₈, separations using these sorbents were compared directly based on olefin product purity, recovery, and throughput. The monolayer AgNO₃/SiO₂ sorbent showed superior separation results for C₃H₆/C₃H₈, and the Ag⁺-exchanged resin showed best results for C₂H₄/C₂H₆. In both cases, over 99% product purities could be obtained at reasonably high recoveries and throughputs. For C₃H₆/C₃H₈ separation on AgNO₃/SiO₂, multiplicity of cyclic steady states were observed within certain regions of feed and purge velocities. Within these regions, two stable cyclic steady states were reached starting from different initial-bed conditions while all operating conditions were identical.