WOLFRAM|DEMONSTRATIONS PROJECT

Non-Ideal Vapor-Liquid Equilibrium (VLE) Modeled by the Margules Equation

deviation from Raoult's law:

positive

negative

diagram

P-x-y

T-x-y

ideal

(

)

non-ideal

ideal

(

)

non-ideal

P-x-y

and

T-x-y

diagrams are generated for one mole of a binary mixture in vapor-liquid equilibrium (VLE). The

P-x-y

diagram is shown at a temperature of 110 °C and the

T-x-y

diagram is shown at a pressure of 1.6 bar. Click and drag the black dot on the diagrams to change the mole fraction of component

and the temperature or pressure. The non-ideal liquid mixture is modeled using the two-parameter Margules model. The interaction between the two components can be attractive (where attractive interactions are stronger than the average of the pure component interactions) and this results in negative deviations from Raoult's law, or the interaction can be repulsive (where attractive interactions are less strong than the average of pure component interactions), and this results in positive deviations from Raoult's law. Vary the degree of interaction using the Margules parameters

and

with sliders. The Margules parameters are used to calculate the activity coefficients

and

. When the Margules parameters are zero, the liquid solution is ideal (Raoult's law) and the activity coefficients equal one. When the activity coefficients deviate significantly from one, the system has an azeotrope. The bar chart on the right displays the relative amounts of liquid (blue) and vapor (green) in equilibrium and the mole fraction of component

in each phase (

for liquid,

for vapor); the relative amounts are calculated using the lever rule. The solid blue curve represents the liquid-phase boundary (bubble point) and the solid green curve represents the vapor-phase boundary (dew point) in the

P-x-y

and

T-x-y

diagrams.