A nonequilibrium model is developed for the simulation of a three-phase distillation process in a column equipped with structured packing. The model is taking into account the mass transfer resistance between all three existing phases. Furthermore, the convective and conductive part of the heat transfer rate is calculated, which is crucial for the precision of the model. The development of the model is strongly connected with experimental investigations of a packed column. When a heterogeneous azeotropic mixture is separated by distillation in a packed column, specific steady states can occur, which cannot be described by the use of an equilibrium model. The observed remarkable column behaviour is caused by the fluid dynamic situation of the two immiscible liquid phases on the structured packing surface. The simulation results are in good agreement with the experimental data of the packed column. (C) 2004 Elsevier Ltd. All rights reserved.