A Model to Describe Associating Mixtures of Structural Isomers

The increased application of renewable resources in the chemical industry leads to more structural isomers with functional groups in the products. Especially the separation of the isomers is currently a challenge since their individual thermodynamic properties are unknown. Experimental investigation is impossible because the components are not available or do not have the required purity. The prediction of the thermodynamic properties of those isomers and their mixtures is therefore of great interest. The Lattice Cluster Theory (LCT) [1] has been frequently applied to predict the phase behavior of branched isomers on the basis of their linear analogues. However, it was only able to describe branched isomers as long as the functional groups did not occupy different positions within the structure. An association model which is able to describe the structure as well as the position of the functional group is desirable.


Therefore, this work show a further development of the Chemical Association Lattice Model (CALM) [2], which was developed on the Flory-Huggins theory. The novel association model is based on the LCT to account for the structure of isomers. The multitude of cluster molecules resulting from the chemical association approach is described by continuous thermodynamics [3].

The model framework and its application to liquid-liquid phase equilibria is presented and discussed in this work. Furthermore, the influence of the individual associating structural isomers on the properties of the mixture is investigated.