Use of Azeotropes To Separate Zeotropic Mixtures
Sometimes azeotropes are useful in separating zeotropic mixtures. An example is acetic acid and water, which do not form an azeotrope. Despite this it is very difficult to separate pure acetic acid (boiling point: 118.1°C) from a solution of acetic acid and water by distillation alone. As progressive distillations produce solutions with less and less water, each further distillation becomes less effective at removing the remaining water. Distilling the solution to dry acetic acid is therefore economically impractical. But ethyl acetate forms an azeotrope with water that boils at 70.4°C. By adding ethyl acetate as an entrainer, it is possible to distill away the azeotrope and leave nearly pure acetic acid as the residue.
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