Physicochemical and thermodynamic properties of binary amine-based deep eutectic solvents for carbon capture

Deep eutectic solvents (DESs) have attracted great interest as a new green alternative to ionic liquids. In order to investigate the potential of using DESs to replace traditional organic solvents in carbon capture processes, it is necessary to understand in detail the physicochemical and thermodynamic properties of DESs before and after CO2 absorption. In this paper, choline chloride was used as the hydrogen bond acceptor and ethanolamine as the hydrogen bond donor to prepare the original DES. Afterward, 5 % mass fraction of morpholine/sarcosine is then added to make two kinds of ternary secondary amine functionalized DESs. Six quaternary DESs were finally prepared by mixing 20 % solvent (water/glycerol/ethylene glycol) with the ternary DESs. Subsequently, the physicochemical properties of DESs, such as melting point, density, viscosity and surface tension, were experimentally determined over the temperature range of 303.15–353.15 K. The properties of ternary and quaternary DESs before and after CO2 absorption were especially predicted and analyzed using different models. It was found that the Vogel-Fulcher-Tamman model was more suitable for forecasting viscosity, and the Pelofsky equation was better for prediction of the relationship between surface tension and viscosity. Based on the experimental data and the solvent critical values predicted by the state equation, the thermodynamic properties of ternary and quaternary DESs before and after CO2 absorption, such as molar volume, isobaric expansion coefficient, lattice energy, activation energy, viscous flow entropy and enthalpy, were derived and analyzed.