5. Vapor-liquid equlibria of two component fully miscible liquids

diagram definition, liquid- and vapor curve, equlibrium, Konovalov’s law, distillation, azeotropic mixture

 

The VLE diagram for a two-component fully miscible liquid system represents the equilibrium relationship between the liquid and vapor phases of the mixture. It provides crucial information about the boiling behavior and separation potential of the mixture during processes like distillation.

Vapor-liquid phase diagram for two fully miscible liquids:

·       for non-dilute solutions there is no mathematical formula for the relationship between them

·       in two dimensions one is the concentration, one is either the temperature or the pressure, the other is kept constant

·       L:

o   boiling point/ liquid curve, below that only liquid, on it the liquid is in equilibrium with the vapor

·       boiling point:

o   the temperature on the boiling point curve, where pressure equals the atmospheric        pressure

·       V:

o   -dew point/vapor curve, above that only vapor, on it the vapor is in equilibrium with        the liquid

·       dew point:

o   -the temperature where the given vapor is in equilibrium with the liquid at the given        pressure

·       X1/X2: mol fractions

o   At a given concentration dew point and boiling point differ

·       The area between the liquid and vapor curves represents a two-phase region where both liquid and vapor coexist.


Konovalov’s rule

·       At a given temperature the more volatile (the one with the lower boiling point) will be more concentrated in the vapor phase

·       At a given temperature the less volatile (the one with the higher boiling point) will be more concentrated in the liquid phase

Distillation

·       separation process that relies on differences in volatility between components in a mixture.

·       we raise the temperature continuously and the concentration of the less volatile material increases

·       the vapor is then condensed to obtain a purer form of the more volatile component.

·       no pure component can be obtained

·       repeated distillation yields a purer product, but less in quantity

           

·       Simple Distillation: Suitable for separating mixtures with significantly different boiling points.

·       Fractional Distillation: Uses a fractionating column to achieve better separation for mixtures with closer boiling points.
 


Azeotropic mixtures:

·       non-Konovalov behavior

  • Azeotropic Mixture: A special type of binary mixture that behaves as a single substance during boiling. At the azeotropic composition, the vapor and liquid have the same composition, and further separation by distillation is not possible.

    • For minimum boiling azeotropes, the azeotropic point has a boiling temperature lower than either of the pure components.

    • For maximum boiling azeotropes, the azeotropic point has a boiling temperature higher than either of the pure components.