This article describes expert aided simulation to solve the problems separation of the liquid mixtures by distillation, identification of separation process state and prediction changes Through an efficient integrating of an expert system for various process models of the liquid mixtures separation and an expert system for model validation and parameters estimation a separation process operation have been studied. The segregation of the databases, knowledge bases and inference engines in the expert system allows us to organize the different models and domain expertise efficiently because each of these components can be designed and modified separately. This simulation integrates data bases for component data, mixture data, vapour pressure and model parameter tables with structured knowledge representation subsystems for separation variable determination, prediction of separation conditions and estimation of process state and its changes. The application is demonstrated through two examples.