Thermodynamics of mixtures with strongly negative deviations from Raoult's law

Vapor pressures of the 1-propanol + di-n-propylamine (DPA) system at six different temperatures between 293.15 and 318.15 K were measured by a static method. The reduction of the experimental data to obtain molar excess Gibbs energies, GE was carried out according to Barker's method, assuming that GE is represented by a Redlich-Kister equation. In the temperature range considered, the mixture shows azeotropic behaviour and negative deviation from the Raoult's law. DISQUAC describes better than the ERAS or UNIFAC (Dortmund version) models the experimental data. The analysis of the mixture structure in terms of the so-called concentration-concentration structure factor, Scc(0) reveals that interactions between unlike molecules occur in such a way that several molecules of amine interact with one molecule of alcohol.