DUAL DIFFUSION AND FINITE MASS-EXCHANGE MODEL FOR ADSORPTION-KINETICSIN ACTIVATED CARBON

A model allowing for the finite mass exchange between the two phases i s proposed for the description of adsorption kinetics in activated car bon. This model based on Do's earlier structural model for activated c arbon involves three mass-transfer processes: pore diffusion, adsorbed phase diffusion, and finite mass interchange between the fluid and ad sorbed phases. The solid phase is heterogeneous, which is characterize d by the micropore size distribution. The interaction between the adso rbate molecule and the micropore is calculated from the Lennard-Jones potential theory. The model developed for nonpolar adsorbates is teste d with the experimental data of seven adsorbates (paraffin gases, arom atics, carbon dioxide, and sulfur dioxide) on pellets of different sha pes and sites and at various operating conditions. The finite kinetics play an important role in the overall kinetics. Failure to account fo r this finite kinetics makes the model unable to describe correctly th e desorption behavior since under such conditions, the ability of the particle to release adsorbed molecules is dictated mostly by the resis tance at the pore mouth of the micropore.