This Demonstration plots the residue curve of a nonideal ternary mixture composed of water ethanol and ethylene glycol Deviation from ideal behavior in the liquid phase is taken into account using the Wilson model in order to compute the activity coefficients Total pressure is equal to 101325 kPa This mixture presents one azeotrope between water and ethanol marked in the ternary diagram by 8808 mole fraction of ethanol and 1192 mole fraction of water Ethylene glycol and the azeotrope are stable and unstable nodes respectively Water and ethanol are two saddle points As you drag the locator the program plots the residue curve passing through the locator position Such a residue curve map computation is useful in the design of extractive distillation columns for waterethanol separations ie ethanol dehydration using ethylene glycol as an entrainer