A complete breakthrough model is proposed and solved in this work to describe the removal of volatile organic compounds from a diluted single-component gas stream passing through a microporous activated carbon fiber monolith (ACFM) under isothermal conditions. All significant parameters are considered in the model, including type of adsorption isotherm, resistance to external gas diffusion, non-instantaneous adsorption kinetics at the external surface and type of gas diffusion within the pore system. n-Butane was employed as the test compound for obtaining the experimental breakthrough curves. The model including non-instantaneous adsorption at the external surface and surface pore diffusion describes properly the experimental adsorption results. (c) 2006 Elsevier Ltd. All rights reserved.