The behaviour of butyl ether as entrainer in extractive distillation for the rupture of the propanone + diisopropyl ether azeotropic mixture is investigated. The vapor-liquid equilibrium of each component with butyl ether has been carried out at 101.3 kPa in order to check the absence of azeotropes. Neither system showed an azeotrope. Thermodynamic consistency of the experimental data was good. The activity coefficients were correlated by means of the van Laar, Wilson, NRTL and UNIQUAC equations. UNIFAC prediction has been also used. As a final part, an experiment of extractive distillation was carried out and a composition of 0.990 in mole fraction of acetone, 0.001 of diisopropyl ether and 0.009 of butyl ether resulted in the head of the column. In conclusion, butyl ether is an excellent solvent for the rupture of the studied azeotropic mixture.