3. Distillation with pressure change
If the composition of the azeotrope AzAB or the relative volatility αAB varies with pressure, a conventional distillation process can be used, introducing no entrainer, which therefore needs neither vaporization nor recovery.
Generally, the composition of the light component A in the azeotropic mixture increases as the pressure decreases, possibly until the azeotrope disappears.
Thus, for the homoazeotrope Tmax water (100 °C) – formic acid (100.8 °C),
xwater = 0.42 at 1 atm (760 mmHg) (Tazeo = 107.3 °C),
xwater = 0.50 to 0.26 atm (200 mmHg) (Tazeo = 71.3 °C),
xwater = 0.58 at 0.13 atm (100 mmHg) (Tazeo = 55.7 °C).
For water-ethanol, the azeotrope disappears below 0.07 atm.
In the pressure-swing distillation process,...
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Distillation with pressure change
Azeotropic distillation
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