Investigation of Steric Effects for Diffusion of Alkanes In Activated Carbon

A concentration-swing frequency response method is applied to study steric effects for mass transfer of hydrocarbons in activated carbon.  We consider alkanes of different geometries: straight chain, branched chain, and cyclic.  Isotherms are measured independently to allow comparison with local isotherm slopes derived from the linearized mass transfer theory.  Micropore (surface) diffusion is determined to be the main controlling mass transfer resistance, and diffusion rates are compared with respect to the size and shape of the adsorbates.  Steric hindrance is found for the cyclic form in comparison to the straight chain form.  Mass transfer rates are measured at different concentrations to establish the concentration dependences of the micropore diffusion coefficients and to permit comparisons with commonly accepted trends.  Prior work on steric hindrance is discussed including for other adsorbent-adsorbate pairs.  Our study provides a complementary treatment of steric effects existing in activated carbons.