Pore-surface diffusion model for batch adsorption processes

A new pore-surface diffusion model (PSDM) for batch adsorption systems has been developed. The new PSDM incorporates pore and surface diffusion into a variable effective diffusion coefficient, but the contributions from both pore and surface diffusion are evaluated independently. This model is compared with two previous models, which were based on a "lumped" effective diffusion coefficient, for which rapid analytical solutions have been developed. A further advantage of the new model is that it incorporates a time dependent surface diffusivity based on surface adsorbate concentration. Previous rapid analytical solutions to the effective pore diffusion models have assumed a constant time independent surface adsorbate concentration. The three models have been compared using four sets of experimental data for the batch adsorption of dyes onto wood and peat.