In analogy to activity coefficient models used in chemical engineering, such as NRTL, UNIQUAC or UNIFAC, the final chemical potential can be split into a combinatorial and a residual (non ideal) contribution.
While UNIQUAC is a first order approximation, COSMOSPACE gives the exact solution of a lattice model in which pairwise molecule surfaces interact.
An alternative is to obtain activity coefficients with a method such as UNIFAC, and the UNIFAC parameters can then be simplified by fitting to obtain the UNIQUAC parameters.
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MOSCED, a model for estimating limiting activity coefficients at infinite dilution
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The UNIQUAC model also serves as the basis of the development of the group contribution method UNIFAC, where molecules are subdivided in atomic groups.
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UNIFAC : A method which permits the volume, surface and in particular,the binary interaction parameters to be estimated.
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A more thermodynamically consistent form of UNIQUAC is given by the more recent COSMOSPACE and the equivalent GEQUAC model.
UNIQUAC |
Although the model is old it has the characteristic feature to describe extrema in the activity coefficient, which modern models like UNIQUAC, NRTL and Wilson cannot.