Relative volatility

The dimensionless relative volatility is the ratio of the volatilities of the components in a binary mixture.

Definition

For binary mixtures, the relative volatility α is defined as:

With the K- factor

With

  • Y: mole fraction of a component in the vapor
  • X: mole fraction of a component in the liquid.

Therefore, can the relative volatility also be written as:

Importance

The relative volatility is an important factor in separation techniques:

  • Large relative volatilities allow easy separation of materials by a distillation or rectification
  • A relative volatility of 1 describes an azeotrope by the two above-mentioned The method can not be separated.

Example

The mixture of chloroform and ethanol exhibits a pronounced azeotrope at about 84 mole percent chloroform and p = 101.325 kPa; here:

  • , the vapor -liquid equilibrium at a minimum, Vapor -liquid equilibrium ( isobaric )
  • Intersect the K- factors (K1 = K2) K- factors
  • Is the relative volatility α = 1 Relative volatility

It will be appreciated that the K -factor and the relative volatility is deduced from the vapor -liquid equilibrium.

Fenske equation
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