Non-random two-liquid model

The Non- Random, Two - Liquid model ( short NRTL equation, dt non- random two-liquid ) is a thermodynamic model of its composition, expressed by the mole fractions, correlates the activity coefficient of a chemical compound mixture.

Since they also use the excess Gibbs free ( excess size of the free enthalpy) NRTL models belong to the class of the gE - models.

Equations

For a binary mixture, the following equations apply:

With

And as well as are parameters that are adjusted to the activity coefficient.

However, most parameters are still on relations

Scaled by the gas constant R and the temperature T, and then adjusting the parameters and.

Temperature -dependent parameters

Is the activity coefficient for a wider temperature range available ( for example from vapor-liquid and at the same time of solid-liquid equilibrium ), as temperature-dependent parameters can be introduced.

Two approaches are commonly used:

Individual terms can be omitted. For example. The logarithmic term is generally used only when the liquid-liquid equilibrium ( miscibility gaps ) need to be modeled.

Origin of the activity coefficients

The activity coefficients required are mostly derived from experimentally determined phase equilibria ( vapor-liquid, liquid-liquid, solid-liquid ) and from heats of mixing. Source of these experimental data are factual databases such as the Dortmund Data Bank. Alternatively, the activity coefficients are determined directly by experiment or prediction models, such as UNIFAC determined.