page_title: Azeotropic distillation
section_title: Distillation of ethanol/water
hierarchical_section_title: Azeotropic distillation / Distillation of ethanol/water
context_page_description: In chemistry, azeotropic distillation is any of a range of techniques used to break an azeotrope in distillation. In chemical engineering, azeotropic distillation usually refers to the specific technique of adding another component to generate a new, lower-boiling azeotrope that is heterogeneous, such as the example below with the addition of benzene to water and ethanol. This practice of adding an entrainer which forms a separate phase is a specific sub-set of azeotropic distillation methods, or combination thereof. In some senses, adding an entrainer is similar to extractive distillation.
context_section_description: A common historical example of azeotropic distillation is its use in dehydrating ethanol and water mixtures. For this, a near azeotropic mixture is sent to the final column where azeotropic distillation takes place. Several entrainers can be used for this specific process: benzene, pentane, cyclohexane, hexane, heptane, isooctane, acetone, and diethyl ether are all options as the mixture. Of these benzene and cyclohexane have been used the most extensively. However, because benzene has been discovered to be a carcinogenic compound, its use has declined. While this method was the standard for dehydrating ethanol in the past, it has lost favor due to the high capital and energy costs associated with it.
  Another favorable method and less toxic than using benzene to break the azeotrope of the ethanol-water system is to use toluene instead.
caption: A Dean-Stark apparatus is used in azeotropic drying or dehydration processes:  1 stirrer bar/anti-bumping granules, 2 still pot, 3 fractionating column, 4 thermometer/boiling point temperature, 5 condenser, 6 cooling water in, 7 cooling water out, 8 burette, 9 tap, 10 collection vessel