Adsorption is an indispensable technology in many industrial processes. In order to enhance the understanding of the process and to optimize its application, simulation is a useful tool. An approach to simulate adsorption of toluene from air in a fixed bed of activated carbon grains is exemplified. A 3D model of the fixed bed is generated by the discrete element method. Computational fluid dynamics simulations are carried out by the Lattice-Boltzmann method. Numerical parameters are calibrated by matching single grain loading curves to experimental data.