Solid-Liquid Equilibria for Hexafluorophosphate-Based Ionic Liquid Quaternary Mixtures and Their Corresponding Subsystems


The present work describes an experimental study and the thermodynamic modeling for the solid-liquid phase diagram of an ionic liquid quaternary system constituted by hexafluorophosphate ([PF6](-)) as the common anion and by 1-methyl-3-propylimidazolium ([C(3)mim](+)), 1-methyl-1-propylpyrrolidinium ([C(3)mpyrr](+)), 1-methyl-3-propylpyridinium ([C(3)mpy](+)), or 1-methyl-1-propylpiperidinium ([C(3)mpip](+)) as the cations. The Modified Quasichemical Model was used to model the liquid solution, and the Compound Energy Formalism was used for the relevant solid solutions. The liquidus projections of the four ternary subsystems (1) [C(3)mim][PF6]-[C(3)mpip][PF6]-[C(3)mpyrr]-[PF6], (2) [C(3)mpy][PF6]-[C(3)mpip][PF6]-[C(3)mpyrr][PF6], (3) [C(3)mpip][PF6]-[C(3)mpy][PF6]-[C(3)mim][PF6], and (4) [C(3)mpyrr][PF6]-[C(3)mpy][PF6]-[C(3)mim][PF6] were predicted using a standard symmetric (for systems 3 and 4) or asymmetric (for systems 1 and 2) interpolation method. In order to test the accuracy of the thermodynamic model, two isoplethal sections were experimentally measured in each of the four ternary systems using differential scanning calorimetry. Overall, agreement was very satisfactory, not requiring fitting of any ternary interaction parameters for the liquid solution model. In each of the four calculated ternary liquidus projections, the region of composition corresponding to room temperature ionic liquid mixtures was determined. The global minimum of the liquidus temperature in the complete composition space was calculated to be about -16 degrees C, with a mole percentage composition of (33.8% [C(3)mpyrr][PF6] + 33.9% [C(3)mpy][PF6] + 32.3% [C(3)mim][PF6]).



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Mirarabrazi, M; Martins, MAR; Pinho, SP; Coutinho, JAP; Robelin, C

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The modeling part of this project was supported by the Natural Sciences and Engineering Research Council of Canada (Discovery Grant RGPIN 435893-2013). The new DSC measurements in the four ternary subsystems were supported by the laboratories CICECO Aveiro Institute of Materials, project POCI-01-0145-FEDER-007679 (ref FCT UID/CTM/50011/2019), and Associate Laboratory LSRE-LCM (ref FCT UID/EQU/50020/2019), both financed by national funds through the FCT/MEC and when appropriate cofinanced by FEDER under the PT2020 Partnership Agreement, and the project AIProcMat@N2020 Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020 (ref NORTE-01-0145-FEDER-000006) supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF). Constructive discussions with Dr. Aimen Gheribi, Prof. YounBae Kang, and Prof. Nick Virgilio were much appreciated.

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