Experimental solubility and density studies on aqueous solutions of quaternary ammonium halides, and thermodynamic modelling for melting enthalpy estimations

• Published in: Journal of molecular liquids 2020-02, Vol.300, p.112281, Article 112281
• Main Authors: Vilas-Boas, Sérgio M., Abranches, Dinis O., Crespo, Emanuel A., Ferreira, Olga, Coutinho, João A.P., Pinho, Simão P.
• Format: Article
• Language: English
• Subjects: COSMO-RS; Melting; PC-SAFT; Quaternary ammonium salts; Solubility
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2019.112281

Aiming to extend the yet limited knowledge on phase equilibria and physical-chemical properties of quaternary alkylammonium halides and their aqueous binary systems, the solubilities of ten salts in water were measured in this work in the temperature range between 293.2 K and 348.2 K along with their densities. The PC-SAFT equation of state was then applied in the description of density as well as water activity coefficients data. The modelling results describe very satisfactorily the experimental data, and the non-associating parameters follow well-defined trends with the molecular weight of the alkylammonium halides. These parameters were applied in the prediction of the solubility data with unsatisfactory results, with mole fraction average absolute deviation (AAD = 0.018), deteriorating with increasing alkyl chain length. However, refitting the binary interaction parameter a much better description is obtained (AAD = 0.0045). COSMO-RS was also applied for the solubility prediction (AAD = 0.025), with poorer results for the chloride salts. After, the melting enthalpies of the quaternary alkylammonium halides were estimated using the PC-SAFT equation, which in spite of their uncertainty, are possibly the best option to perform solid-liquid equilibrium analysis of utmost importance when designing and screening new deep eutectic mixtures based on these compounds. [Display omitted] •Densities and solubilities are measured for ten alkylammonium halides in water at several temperatures.•The PC-SAFT describes accurately density and water activity coefficient data.•PC-SAFT non-associating parameters follow well-defined trends with the molecular weight of the salts.•Solubilities are calculated with accuracy fitting only a PC-SAFT binary interaction parameter.•The procedure proposed allows the estimation of reliable melting enthalpies of the quaternary alkylammonium halides.