Abstract
The SAFT equation of state [1,2,3,4] constitutes one of the most sophisticated and successful molecular-based approaches for thermo-physical property prediction of fluids. However, most versions of SAFT are based on Wertheim’s first-order thermodynamic perturbation theory (TPT1) [5], and as consequence the formation of any type of ring, by covalent bonding, or association (inter or intra-molecular) is neglected. The applicability of SAFT in its standard formulation is hence by design, better suited to systems where the effects resulting from the formation of rings are not significant.
Although the extent of intramolecular association alone is a weak function of density, when the competition of this effect with intermolecular association is considered, the dominant association type becomes increasingly density dependent. The direct result of the formation of intramolecular hydrogen bonds (IMHB) is the decrease of the availability of the molecule sites to bond with other molecules. Accounting for the competition between inter- and intra-molecular association is crucial in applications that rely on solubility predictions of molecules that allow IMHB, such is the case of solvent design for active pharmaceutical ingredient processing.
Sear and Jackson [6] and Ghonasgi et al. [7] developed theories to account for intramolecular in addition to intermolecular association, following the original theory of Wertheim [5]. In the current work, intramolecular association in chain molecules of heterogeneous Mie segments is considered through an algebraic approach. By extending and adapting the theory described in [6] to multiple associating sites and component mixtures, the SAFT framework can be modified to account for the competition between intra and intermolecular association. The results of the prediction of thermodynamic properties using SAFT for systems of interest to the pharmaceutical industry accounting and neglecting ring formation are presented and discussed.
References
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