The rigorous modelling of pervaporation, especially in professional software environment, plays a high practical importance if hybrid separation processes containing membrane units are to be designed. In this work a methodology is recommended and presented for such design problems. This methodology consists of the following steps: laboratory pervaporation experiments, estimation of the parameters needed for the modelling of the pervaporation, and finally the double verification of the parameters. The parameter estimation is handled as a mixed integer nonlinear programming (MINLP) problem and professional flowshecting simulator is also applied in the double verification step. Following this methodology, reliable parameters of the pervaporation needed for rigorous modelling can be determined. The pervaporation module with the reliable parameters in professional software environment enables the design of complicated separation processes, e.g., hybrid separation processes containing pervaporation. (C) 2007 Elsevier B.V. All rights reserved.