Thin-film evaporators are often used for separations. Despite the long-standing research in this area, there is still a lack of reliable data on measurements on test systems that could be used for model development and validation. In this research, therefore, the partial evaporation of the binary mixtures of ethylene glycol and water as well as water and methanol is studied in a laboratory-scale thin-film evaporator operated in counter-current mode. Two types of equilibrium stage models of the separation process are tested, in which the process is described as open and closed evaporation, respectively. The results show that, especially at low vapor streams, a considerable rectification effect occurs in the thin-film evaporator that can only be modeled using the closed evaporation approach. The equilibrium stage approach is sufficient for describing the data from the present work. (C) 2007 Elsevier B.V. All rights reserved.