Vapor-liquid equilibria at 363.15K, and excess enthalpies in the temperature range 363.15-413.15 K of binary systems containing the ionic liquids 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [BMPYR](+)[BTI](-), 1-hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [HMPYR](+)[BTI](-), and 1-octyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [OMPYR](+) [BTI](-), have been measured. The experimental data were used for fitting the group interaction parameters between the pyrrolidinium cation and the main groups ACH and ACCH(2). The experimental results are compared with the predictions of modified UNIFAC (Dortmund). Furthermore the current state of modified UNIFAC matrix for ionic liquids, typical results, and the application for process development will be presented. (C) 2010 Elsevier B.V. All rights reserved.