Experimental solubility and density studies on aqueous solutions ofquaternary ammonium halides, and thermodynamic modelling formelting enthalpy estimations

Abstract

Aiming to extend the yet limited knowledge on phase equilibria and physical-chemical properties of quaternaryalkylammonium halides and their aqueous binary systems, the solubilities of ten salts in water were measured inthis work in the temperature range between 293.2 K and 348.2 K along with their densities. The PC-SAFT equa-tion of state was thenapplied in the description of density as well as water activity coefficients data. The model-ling 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 inthe 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 thebinaryinteraction param-eter a much better description is obtained (AAD = 0.0045). COSMO-RS was also applied for the solubility predic-tion (AAD = 0.025), with poorer results for the chloride salts. After, the melting enthalpies of the quaternaryalkylammonium halides were estimated using the PC-SAFT equation, which in spite of their uncertainty, are pos-sibly the best option to perform solid-liquid equilibrium analysis of utmost importance when designing andscreening new deep eutectic mixtures based on these compounds.