Heterogeneous azeotropic distillation in packed columns is often very diffi
cult because three phases, i.e., two liquid phases and one gas phase, can o
ccur. In this type of distillation, also known as three-phase distillation,
the second liquid phase can change the mass transfer efficiency of the pac
king in a significant way. The present paper focuses on simple distillation
experiments with the mixture acetone/water/toluene. The evaluation of thes
e experiments helps us better understand the effects of a second liquid pha
se on the mass transfer in a packed distillation column.