An accurate knowledge of the thermophysical properties and phase behaviour of
fluid mixtures is essential for the reliable design of products and processes across a wide
range of chemical engineering applications, varying from the processing of petroleum
fluids to the manufacturing of pharmaceuticals. Thermodynamic tools and, in the
context of this work, group contribution (GC) methods are predictive approaches
that are expected to play an important role in meeting these industrial needs. The
principal focus of the work presented in this thesis is the development of a novel GC
method based on the statistical associating fluid theory (SAFT): the SAFT-γ Mie
approach. The method is developed based on a detailed molecular model and a realistic
intermolecular potential, the Mie potential with variable attractive and repulsive
ranges, for the description of interactions at a molecular level. Over the past decade,
an increasing research effort has been devoted to developing formalisms that couple
the accuracy of the SAFT equation of state (EoS) with the predictive capabilities of
group contribution approaches. In the development of such methods one aims to overcome
the limitations inherent to GC approaches based on activity coefficient models,
such as in the well-established universal quasi-chemical functional group activity coefficient
(UNIFAC) approach. A more recent landmark has been the development of
heteronuclear methods within SAFT. The SAFT-γ EoS based on the square-well (SW)
potential has been shown to describe accurately the phase behaviour of a wide variety
of fluids. In the work presented in this thesis, SAFT-γ SW is applied to the study of
the fluid phase behaviour of aqueous solutions of hydrocarbons. These mixtures are of
high industrial relevance, and the accurate representation of their highly non-ideal nature
is very challenging from a theoretical perspective. The SAFT-γ method is shown
to perform comparatively well in predicting the behaviour of the systems examined.
Nonetheless, some challenges are identified, such as the description of thermodynamic
derivative properties and the description of near-critical fluid phase behaviour, where
the performance of the method is shown to be less accurate. These challenges partially
arise from the simplistic intermolecular square-well potential employed within SAFT-γ
SW, which allows for a rigorous theoretical development, but fails to reproduce accurately
finer aspects of the thermophysical behaviour of fluids, such as second-order
derivative thermodynamic properties.
These challenges are tackled here with the development of the SAFT-γ Mie GC
approach, based on the versatile Mie intermolecular potential and a third-order treatment
of the thermodynamics of the monomer segments. The SAFT-γ Mie method
is applied to the study of the properties of two chemical families, n-alkanes and 2-
ketones, and it is shown that a significant improvement over existing SAFT-based
group contribution approaches can be achieved in the description of the pure component
phase behaviour of the compounds studied. Moreover, the application of a realistic intermolecular potential is shown to allow for an excellent description of
second-order derivative thermodynamic properties, and the accurate treatment of the
intersegment interactions is shown to improve the performance of the method in the
description of the near-critical fluid phase behaviour. The predictive capability of the
method is demonstrated in the description of mixture fluid phase behaviour and excess
thermodynamic properties in a predictive manner. Given the promising performance
of the SAFT-γ Mie EoS, the method is applied to the case study of the solubility
of two active pharmaceutical ingredients in organic solvents. The method is shown
to satisfactorily predict the solubilities of the mixtures considered, based on limited
experimental data for simple systems. Given the complexity of the mixtures studied,
the performance of the SAFT-γ Mie is considered very encouraging and shows that
there is great potential in the application of the method to this challenging field.