About Azeotrope.info

This application brings for you azeotropic data (azeotrope boiling point/temperature and composition), based on vapor-liquid equilibrium calculations. So the program does not provide stored experimental data, but predicts them theoretically.

Method of calculation

At an azeotropic point the composition of vapor- and liquid phases are identical (x_i = y_i), and the bubble- and dew point curves have a local extrema.

Take an objective function that measures the relative deviation of the compositions between the vapor- and liquid phases:

f_i = (x_i - y_i) / x_i

At every x points in the composition space, where f_i = 0 must be an azeotropic point. (Except the corner points representing the pure components (i), where x_i = 1 and x_j≠i = 0.) The program uses multi-variate Newton-Raphson search to locate these points.

The composition of the vapor phase is calculated according to the modified Raoult's law:

p_i = γ_i • p_sat.,i • x_i

y_i = p_i / Σ_j=1→N p_j

where:

p_i is the partial pressure of component i in the vapor phase of the mixture
γ_i (gamma) is the activity coefficient of component i in the liquid mixture
p_sat.,i is the vapor pressure of saturated pure component i
x is the liquid phase mole fraction of component i
y is the vapor phase mole fraction of component i

The program uses the UNIFAC (modified, Dortmund) model for calculating the activity coefficient.

Find more information about azeotropes at Wikipedia