New approximate model for nonlinear adsorption and diffusion in a single particle

A new approximate model of the general adsorption and diffusion model is derived that describes gas and adsorbed phase dependent diffusion in a single spherical sorbent particle governed by a nonlinear adsorption isotherm. This new approximate model compares very well with the exact (numerical) solution of the general adsorption and diffusion model over a wide range of (Langmuir) isotherm nonlinearity, and pore and surface diffusivities. Thus, it provides a significant advantage in terms of computation compared to the exact (numerical) model. This new model is simple to use and far superior to the popular linear driving force model, which severely underpredicts the uptake curve (compared to the new model) unless the adsorption isotherm is very favorable and the bulk concentration is low, approaching the Henry's law region of the isotherm. (C) 1997 Elsevier Science Ltd.