Extractive Distillation is an important tool for the separation of isomers and close boiling species. An extractive distillation solvent is added to the column increasing the relative volatility of the close boiling species allowing distillation to be utilized. Several applications of extractive distillation have been successfully commissioned. Two of the applications are aromatics and butadiene which will be discussed.

Design concerns for extractive distillation include fouling potential, corrosion, multiple liquid phases and foaming. The design of the tower internals must address each of these issues for the application to be a success and have a reliable on steam time between planned outages. Each of these issues will be discussed for the each application.