Thermodynamic phase diagrams were investigated that play a very important role in designing the separation of furfural from the ternary mixtures furfural + 5-methylfurfural + water and furfural + acetic acid + water. The saturation vapor pressure of 5-methylfurfural in the temperature range from (359.95 to 450.19) K is reported, as well as VLE data for the two binary systems furfural + 5-methylfurfural and furfural + acetic acid at two pressures and LLE data for furfural + 5-methylfurfural + water at room temperature. The activity coefficients at infinite dilution were determined for water in 5-methylfurfural at a few temperatures by using an ebulliometric technique. Binary interaction parameters of UNIQUAC and NRTL local composition models were evaluated in order to simulate the separation of furfural from both ternary mixtures by means of a rectification process. Binary azeotropic points were estimated for the 5-methylfurfural + water system by using both models as well as residue curves of both ternary systems.