(574g) Understanding the Role of Intermolecular Forces in Molecular-Based Equations of State: 20 Years of the Soft-SAFT Equation

Vega, L. F. - Presenter, Gas Research Center. The Petroleum Institute
Llovell, F., IQS School of Engineering. Universitat Ramon Llull
Blas, F. J., University of Huelva
Vilaseca, O., MATGAS Research Center
Coutinho, J. A. P., CICECO, Universidade de Aveiro
More than twenty five years have passed since the first paper published on the development of what it is known today as the SAFT equation of state or the SAFT approach1-2 (from the Statistical Associating Fluid Theory). SAFT was developed, from the very beginning, to describe the thermodynamic properties and phase behavior of associating systems, naturally extended to oligomers, polymers and other systems with highly directional and short range attractive forces, for which the cubic equations of state fail to provide an adequate description. The original equation was developed using a hard fluid as a reference term, while dispersion was added as a perturbation. However, it was very soon discovered that more refined reference terms were needed for accurate predictions of complex systems, leading to the development of soft-SAFT-LJ3, soft-SAFT4-6 and SAFT-VR7 in the mid-late 90’s, in which the reference term take into account repulsion and dispersion forces. In 2001 PC-SAFT8 provided a different approach in which the dispersion term was added as a perturbation to a chain reference term. SAFT-gamma-Mie9 was recently developed aiming at having a soft, flexible, reference term, generalizing the SAF-LJ and soft-SAFT EoS. During these years different version of SAFT have been implemented by different authors and the approach has been widely used to model highly non ideal systems. There are several excellent reviews on this topic.10-12

This talk will first provide an overview on how having the right physics with the adequate level of approximations has made soft-SAFT one of the most accurate, yet simple, versions of SAFT, twenty years after the first paper on soft-SAFT was published. In addition, the built in theory in the equation allows its extension to calculate different properties of the systems, delivering a global equation for the characterization of thermophysical properties. Today, soft-SAFT is a robust tool for calculating critical, phase, interfacial, transport and thermodynamic derivatives properties of associating fluids and polymers. Examples on the relationship between the intermolecular forces description in the equation and the performance of the equation will be provided, including systems such as ionic liquids, aqueous solutions and deep eutectic solvents, highlighting the robutness of the equation. We will also tackle some of remaining challenges and the opportunities on moving SAFT from academia to industry and backwards.


However, there are still remaining challenges and opportunities for developments before soft-SAFT (as any SAFT equation) can be truly considered a standard tool in industrial process development and design and these will also be addressed in this presentation.

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