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Category: Selected Topics

The knowledge of thermodynamic properties of complex mixtures used in chemical industry are of prime importance to design and understand chemical engineering processes, such as distillation, extraction, absorption, etc.

Traditional methods used to correlate and predict the thermodynamic behavior of such systems, although useful, usually fail in predicting the behaviour of the system far away from state conditions at which parameters has been adjusted.

This is essential to study the thermodynamic behavior of a system at extreme conditions (high temperatures and pressures), at which experiments are very difficult and expensive to be performed. In this context, molecular modelling techniques constitute a powerful tool to understand and predict the thermodynamic properties and phase equilibria of the target system.

The main goal of this research line is the use and development of statistical mechanical theories for describing thermodynamic properties, including phase behavior, of complex fluid mixtures, such as associating substances and chain-like molecules.

Our group (in collaboration with the Molecular Modelling Group of Dr. Lourdes Vega, Instituto de Ciencia de Materiales, CSIC, Barcelona, Spain) has developed the Soft-SAFT equation of state, which is based on the Statistical Associating Fluid Theory (SAFT) formalism.

The SAFT approach is nowadays considered one of the most sophisticated and versatile molecular-based equations of state for predicting the phase behavior of complex mixtures (hydrocarbons, surfactants, water, polymers, refrigerants, etc.).

One of the main results of the group has been the formulation of the Soft-SAFT equation of state, which provides a useful tool for predicting phase equilibria of mixtures of associating and non-associating chain-like molecules.

The approach has been also applied to address some specific properties of substances of industrial interest. In this context, we have obtained trasnferable parameters for the n-alkane homologous chemical family, which allows to obtained the thermodynamic behavior of long-chain molecules in a purely predictive way.

The most important contributions are summarized below:

• Development of the Soft-SAFT molecular-based equation of state.
• Vapor-liquid equilibria of associating and non-associating Lennard-Jones chains.
• Phase behavior of binary and ternary mixtures of alkanes.

• Critical behavior and partial miscibility phenomena of binary mixtures of n-alkanes.

• Tricritical phenomena in n-alkane mixtures.

• Extension of the SAFT-HS approach to deal with branched chains.

• Development of the Soft-SAFT Dimer approach for predicting the vapor-liquid equilibria of long-chain molecules.