Effect of temperature and composition on physical properties of deep eutectic solvents based on 2-(methylamino)ethanol – measurement and prediction

Abstract

Novel deep eutectic solvents were synthesized using 2-(methylamino)ethanol as hydrogen bond donor with tetrabutylammonium bromide or tetrabutylammonium chloride or tetraethylammonium chloride as hydrogen bond acceptors. Mixtures were prepared at different molar ratios of 1:6, 1:8 and 1:10 salt to alkanolamine and then Fourier Transform Infrared Spectroscopy measurements were performed to confirm hydrogen bonds interactions between components. Moreover, thermal properties such as melting points and thermal stability of deep eutectic solvents were determined and described. Each of important physical properties, including densities, viscosities, refractive indices and sound velocities at the temperature range of 293.15–333.15 K and the pressure of 0.1 MPa, were measured and discussed. The effect of hydrogen bond acceptor to hydrogen bond donor molar ratio, anion and length of alkyl chain for each synthesized salt according to their properties was evaluated. Additionally, the experimental values of each physicochemical parameter were compared with the predicted ones calculated using models recommended in literature. The main aim of this work was to assess the suitability of existing mathematical models for predicting the physicochemical properties of novel alkanolamine-based DESs. Empirical correlations for approximating phase behaviour or flow properties for DES systems are used in many procedures for design materials used of carbon-dioxide capture purposes. The obtained results indicate that in the case of deep eutectic solvents based on 2-(methylamino)ethanol, in the absence of any experimental data, the best models for density prediction are the bonding group interaction contribution method and the group contribution model. For modelling of the refractive index it has been confirmed that a method based on the critical properties is the most satisfying. However, for the viscosity and speed of sound, the absolute average relative deviations for the methods based on critical properties exceed the measurement uncertainties found in practice. Therefore, they do not seem suitable for an accurate estimation of these properties for deep eutectic solvents based on 2-(methylamino)ethanol.