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User:WilfriedC/Playground/NRTL

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The Non-Random Two Liquid model[1] (short NRTL equation) is a activity coefficient model that correlates the activity coefficients with the composition of a mixture of chemical compounds, expressed by mole fractions .

Equations

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For a binary mixture the following equations[2] are used:

with

and

and as well as are fittable parameters. In most cases the parameters

and

are scaled with the gas constant and the temperature and then the parameters and are fitted.

Temperature dependend parameters

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If activity coefficients are available over a larger temperature range (maybe derived from both vapor-liquid and solid-liquid equilibria) temperature-dependend parameters can be introduced.

Two different approaches are used:

Single terms can be omitted. E. g., the logarithmic term is only used if liquid-liquid equilibria (miscibility gap) have to be described.

Parameter determination

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The NRTL parameters are fitted to activity coefficients that have been derived from experimentally determined phase equilibrium data (vapor-liquid, liquid-liquid, solid-liquid) as well as from heats of mixing. The source of the experimental data are often factual data banks like the Dortmund Data Bank. Other options are direct experimental work and predicted activity coefficients with UNIFAC and similar models.

Literatur

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  1. ^ Renon H., Prausnitz J. M., Local Compositions in Thermodynamic Excess Functions for Liquid Mixtures, AIChE J., 14(1), S.135-144, 1968
  2. ^ Reid R. C., Prausnitz J. M., Poling B. E., The Properties of Gases & Liquids, 4. Edition, McGraw-Hill, 1988