Conclusions We have performed a series of simulations to investigate theeffect of aqueous phase ethanol concentration in the selectiveextraction of ethanol using either zeolites or liquid solvents. Thesesimulations have shown that the formation of ethanol/water aggre-gates plays a key role in the effect of concentration on the partitioncoefficient. The varying degrees of spatial confinement of theseaggregates lead to differences between the zeolite and the solventsystems with the smallest aggregates formed in the rigid zeo-lite framework, promoting high selectivities at low concentrationswhile leading to sharp decreases in both the partition coefficientand the selectivity at higher concentrations. In the more flexible sol-vent systems, particularly the sterically accessible decan-1-ol, theselectivity is reduced by the improved ability of water to form mul-tiple hydrogen bonds with the solvent molecules and the formationof larger ethanol/water aggregates. These aggregates lead to flat orslightly increasing partition coefficients at higher concentrations.These results indicate that the best balance of selectivity and capac-ity can be achieved by an extraction system that has a high affinityfor ethanol but can limit the growth of ethanol/water aggregates,either through a very rigid structure, as in the case of the zeo-lite systems, or through steric hindrance around hydrogen-bondinggroups, as observed in the solvent extraction using decan-4-ol.