Extractive distillation
Distillation of non-ideal mixtures

The term extractive distillation is reserved for the process where the entrainer E is fed continuously to a given location in the column (boiler, intermediate tray or overhead tray) other than that of the A-B mixture.

The addition of E amplifies the difference in volatility between constituents, and thus accentuates the driving force of separation. It can even reverse the relative volatilities, so that the normally less volatile component (B by convention) can follow the path of the lighter components.