The Role of Polyfunctionality in the Formation of [Ch]Cl-Carboxylic Acid-Based Deep Eutectic Solvents


Aiming at providing an extensive characterization of the solid-liquid equilibria (SLE) of deep eutectic solvents (DESs), the phase diagrams of nine eutectic mixtures composed of choline chloride ([Ch]Cl) and (poly)carboxylic acids, commonly reported in the literature as DESs, were measured experimentally. Contrarily to the behavior reported for eutectic mixtures composed of [Ch]Cl (hydrogen-bond acceptor, HBA) and monofunctional hydrogen-bond donors (HBD) such as fatty acids and fatty alcohols, which have recently been shown to be almost ideal mixtures, a significant decrease of the melting temperature, at the eutectic point, was observed for most of the systems studied. This melting temperature depression was attributed to a pronounced nonideality of the liquid phase induced by the strong hydrogen-bond interactions between the two mixture components. Perturbed-chain statistical associating fluid theory (PC-SAFT) was used to describe these interactions physically. PC-SAFT allowed accurately modeling the experimental phase diagrams over the entire concentration and temperature ranges. Depending on the kind of mixture, up to two temperature-independent binary interaction parameters between HBA and HBD were applied. The PC-SAFT approach was used to provide trustworthy information on the nonideality of the liquid phase (expressed as the activity coefficients of HBA and HBD) as well as to estimate the eutectic points coordinates. The experimental data along with the modeling results allowed us to infer about the importance of the HBD's chemical structure on the formation of [Ch]Cl-based DESs.



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Crespo, EA; Silva, LP; Martins, MAR; Bulow, M; Ferreira, O; Sadowski, G; Held, C; Pinho, SP; Coutinho, JAP

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This work was developed in the scope of the project CICECO - Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (ref. FCT UID/CTM/50011/2013) and Associate Laboratory LSRE-LCM, POCI-01-0145-FEDER-006984 (ref. FCT UID/EQU/50020/2013), both financed by national funds through the FCT/MEC and when appropriate cofinanced by FEDER under the PT2020 Partnership Agreement. This work is also a result of project "AlProc-Mat@N2020 - Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020", with the reference 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). M.A.R.M and E.A.C acknowledge FCT for the Ph.D. grants SFRH/BD/87084/2012 and SFRH/BD/130870/2017, respectively. FCT is also acknowledged for funding the project DeepBiorefinery (PTDC/AGRTEC/1191/2014). C.H. gratefully acknowledges financial support from the Max-Buchner Research Foundation and from German Science Foundation (DFG), grant HE 7165/7-1.

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