Separation of dilute ethanol-water mixtures in a fixed bed of bi-dispersed hydrophobic adsorbent, silicalite, is considered. The column dynamics are well described with a differential model accounting for axial dispersion, external him mass transfer and intraparticle diffusion. Diffusion within the solid is firmly controlled by transport through the liquid filled non-selective macropores giving access to the selective micropores of the embedded hydrophobic crystals. A sensitivity analysis indicates that, given the adsorption isotherm, all the mass transfer parameters can be estimated or predicted a priori. The model is verified against a small scale adsorption column making due allowance for the entrance and exit effects; such effects are frequently ignored but are shown here to be significant with small columns.