Adsorption and diffusion behavior of ethane and ethylene in sol-gel derived microporous silica

High surface area silica (500 m(2)/g) was synthesized by the sol-gel method from tetraethyl orthosilicate. The total porosity of the sample was 37% and most of the pores were well below 2 nm in size. The adsorption characteristics of ethylene and ethane in the silica were measured from 300-350 K by gravimetry, and Langmuir adsorption constants and enthalpies and entropies of adsorption were determined. Quasielastic neutron scattering was used to determine the translation and rotational diffusivities of both adsorbates from 200-270 K. Based on the adsorption and translational diffusion characteristics of ethylene and ethane, separation factors of 1.1-2 for olefin to paraffin are predicted.