Group contribution methods refrigerants

In many cases, it is possible to replace environmentally hazardous chemicals with more benign species without compromising the technical and economic performance of the process. Examples include alternative solvents, polymers, and refrigerants. Group contribution methods have been conunonly used in predicting physical and chemical properties of synthesized materials. Two main frameworks have... 

Unreliable results are obtained for group contribution methods in the case, if a large number of functional groups have to be taken into account, as in the case of pharmaceuticals or when the molecule shows groups such as. -C(Cl)(F)(Br) as for example, in refrigerants. But also in these cases similar problems are observed for other approaches, for example, the quantum-chemical methods. 

Summary. Over the last two decades, the UNIFAC group contribution method has come to the fore in the prediction of vapor-liquid equilibria. In order to apply it to refrigerant mixtures, it was necessary to implement additional structure groups, whose interaction amongst each other and with the old groups had to be described by fitting the relevant parameters with respect to measurement data. This led to the problem of minimizing an objective function with approx. 200 variables. 

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