Experiments and Thermodynamic Modeling of the Solubility of Carbon Dioxide in Three Different Deep Eutectic Solvents (DESs)

Carbon capture and storage is needed to reduce the anthropogenic emissions of carbon dioxide (CO2) in atmosphere. Deep eutectic solvents (DESs), due to their low vapor pressure and environmentally benign nature are possible solvents for the carbon capture step. In the present study, the solubility of CO2 in three DESs, namely, reline (choline chloride and urea in a 1:2 molar ratio), ethaline (choline chloride and ethylene glycol in a 1:2 molar ratio), and malinine (choline chloride, malic acid, and ethylene glycol in a 1.3:1:2.2 molar ratio) has been studied in a temperature range of (309 to 329) K at pressures up to 160 kPa. Henry's constants for CO2-DES systems have been determined under these conditions with values in the range of (3.7 to 6.1) MPa (on a molality basis). Thermodynamic modeling using a modified Peng-Robinson equation of state was used to correlate the experimental data. Results showed excellent agreement with a maximum average absolute relative deviation of 1.6% calculated over the complete set of data. The calculated Gibbs free energy, enthalpy of dissolution, and entropy of dissolution show that entropy of the system falls as a result of gas absorption. the CO2 absorption is exothermic and the entropy of the system falls as a result of gas absorption.