New sorbents for olefin/paraffin separations and olefin purification for C₄ hydrocarbons

New adsorbents for olefin/paraffin separations are synthesized by incipient wetness impregnation and ion exchange of Ag⁺ cations on high-surface-area substrates. The separation/purification is achieved by selective adsorption of olefins and/or dienes by π-complexation. It was shown that the monolayer AgNO₃/SiO₂ sorbent has a selective adsorption ratio of 8.33 for butene/butane at 70 °C and 1 atm. The isotherm linearity for olefin is ideally suited for cyclic adsorption-desorption processes. Moreover, the performance of the π-complexation sorbent (AgY zeolite) for the purification of butene by removal of trace amounts of butadiene was found to be superior to that of sorbents based on physical adsorption (5A zeolite and NaY). It was also shown that the Horvath-Kawazoe (H-K) model (using the Cheng-Yang version for spherical pores and correction for isotherm nonlinearity) is capable of predicting the adsorption behavior of the C₄ hydrocarbons on 5A zeolite. Because the H-K model only involves dispersion forces, it underpredicts for gas-solid systems in which other forces also exist such as electrostatic and π-complexation. C₄H₆/C₄H₈ on 5A zeolite is one of these systems.