The excess volumes of protic ionic liquids and its significance to their thermodynamic modelling


With the increasing number of applications being reported for protic ionic liquids (PILs), there is a demand for the development of thermodynamic models that can accurately describe their thermophysical properties and phase equilibria, with equations of state (EoS) derived from the Statistical Associating Fluid Theory (SAFT) being amongst the best. This work aims at discussing the development of such models and the advantages of not using the pseudo-pure component approach commonly adopted in literature, but instead using an individual component approach as previously proposed for Deep Eutectic Systems (DES). Although both PILs and DESs are highly non-ideal mixtures of Bronsted or Lewis acids and bases, PILs are shown to exhibit large negative excess molar volumes when compared to DESs that prevent the direct prediction of the PIL properties by modelling it as a mixture of its precursors, using an individual component approach. To overcome this limitation, and to highlight the importance of being aware of such characteristic of the PILs when developing new models, a simplified volume-shift type correction is applied in the framework of PC-SAFT EoS to provide a more accurate modelling of PILs density data. The implemented correction is shown to increase the accuracy and predictive ability of the model, and its limitations are discussed, suggesting the need for additional experimental data (e.g., on the quantification of the different species present) for the development of robust and general thermodynamic models for PILs (C) 2021 Elsevier B.V. All rights reserved.



subject category

Thermodynamics; Chemistry; Engineering


Crespo, EA; Silva, LP; Carvalho, PJ; Coutinho, JAP

our authors


This work was developed within the scope of the project CICECO - Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. E. A. Crespo and L. P. Silva acknowledge FCT for their Ph.D. grants SFRH/BD/130870/2017 and SFRH/BD/135976/2018, respectively. P. J. Carvalho acknowledges FCT for his contract under the Investigator FCT 2015 contract number IF/00758/2015.

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