Steam Distillation of a Mixture of Hydrocarbons

Consider a binary mixture of the hydrocarbons -octane and -dodecane. The normal boiling point of this mixture is well above 100° C. However, if one adds water to the mixture, it is possible to separate the hydrocarbons at temperatures below 100° C by a method known as steam distillation.

You can change the initial mass of the three compounds in the still. The Demonstration will plot the concentration and temperature profiles. The blue and magenta curves are the composition of the -octane and -dodecane on a water-free basis. Indeed, the distillate is composed of two immicible phases (the organic and aqueous phases). The light brown curve is the water mole fraction in the distillate.

Initially, the distillate is composed of water and octane. At later stages, it contains dodecane and water.