Mass Transfer - Engineering

Q1:

Azeotropism for ethyl alcohol-water system disappears by

A increasing temperature

B decreasing pressure

C increasing pressure

D no means

ANS:B - decreasing pressure

Azeotropism for the ethyl alcohol-water system disappears by increasing pressure. Here's why: Azeotropes are mixtures of liquids that have constant boiling points and compositions. In the case of the ethyl alcohol-water system, the ethanol-water azeotrope forms a constant-boiling mixture where the composition of the vapor phase is the same as that of the liquid phase. For the ethanol-water system, the azeotrope occurs at approximately 95.6% ethanol by mass, with a boiling point of around 78.1°C at atmospheric pressure. By increasing the pressure, the boiling points of the components increase. This change in boiling points disrupts the azeotropic behavior, causing the azeotrope to disappear. As a result, at higher pressures, the ethanol and water components of the mixture can be distilled separately without forming an azeotrope.