A GRAPHICAL-METHOD FOR DETERMINING PORE AND SURFACE DIFFUSIVITIES IN ADSORPTION SYSTEMS

The dynamics of adsorption in a single particle was modeled using two different mathematical formulations: two intrinsic diffusional resistances (macropore and surface diffusion) and one apparent diffusional resistance (pore diffusion). The relationship between the apparent and intrinsic diffusivities was determined and found to be a function of the adsorption isotherm nonlinearity. By combination of this relationship with an analytical solution of the pore (apparent) diffusion model, a method was developed whereby the macropore and surface (intrinsic) diffusivities could be determined directly from experimental adsorption uptake data without the need for any model fitting. This simple method was applied to experimentally measured adsorption dynamics of sulfur dioxide (Freundlich isotherm) and n-butane (Langmuir isotherm) on activated carbon, and was found to give macropore and surface diffusivities similar to that obtained using a full model fit.