Carbon capture and storage is needed to reduce the anthropogenic emissions of carbon dioxide (CO 2 ) 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 CO 2 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 CO 2 −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 the CO 2 absorption is exothermic and the entropy of the system falls as a result of gas absorption.

Deep eutectic solvents (DESs) are novel solvents that have shown the ability to capture carbon dioxide from flue gases. Thermodynamic modeling is needed to validate the experimental vapor–liquid equilibria (VLE) of the CO2–DES systems. To establish thermodynamic models of these solvents, their critical properties must be estimated. In the present study, a combination of the modified Lydersen–Joback–Reid (LJR) method and the Lee–Kesler mixing rules has been applied to estimate the critical properties of 39 different DESs. Normal boiling temperatures and acentric factors have also been determined. The accuracy of this method has been tested by comparison of theoretical densities determined from the estimated critical properties with experimental values. Absolute deviations ranging from 0 % to 17.4 % were observed for the estimated density values. An overall average absolute deviation of 4.9 % was observed for the studied DESs. Absolute deviations for DESs consisting of aliphatic precursors ranged from 0 % to 9.5 %, whereas for DESs consisting of at least one aromatic precursor, these ranged from 5.8 % to 17.4 %. The accuracy fell as the percentage of hydrogen-bond donors (HBD) increased. The method was also found to accurately take into account the variation in density due to a temperature change.

Potassium carbonate is considered a promising solvent for carbon dioxide (CO2) capture as it is cost-effective and environmentally benign when compared to traditional amine-based solvents. In order to increase absorption capacity, the use of concentrated potassium carbonate solvent has been proposed in which CO2 absorption results in precipitation of bicarbonate. Understanding the formation of the solids in that system is important if this is to be used for CO2 capture. In this work, the precipitation behavior in the ternary system of potassium carbonate–potassium bicarbonate–water was studied in a batch cooling crystallizer equipped with Focused Beam Reflectance Measurement (FBRM) and an Optimax workstation. The solubility data were validated using a regressed Electrolyte Non-Random Two Liquid (ENRTL) activity model developed in Aspen Plus. The precipitate was determined as kalicinite with hexagonal prism shape by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The nucleation kinetics were evaluated using the metastable zone width method and induction time method. Results indicated that in the studied ternary system there were two separate regions corresponding to different nucleation mechanisms, which were defined by the cooling rate. The supersaturation of potassium bicarbonate and the concentration of potassium carbonate determined the nucleation kinetics. On the basis of the calculated nucleation kinetics, the continuous growth mechanism of the crystals was further examined using the surface entropy value and SEM images.

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Carbon capture and storage (CCS) is one of the technologies needed to reduce anthropogenic emissions of CO 2 in the atmosphere. Protic ionic liquids (PILs) are potential nonaqueous solvents that can combine the benefits of ionic liquids (ILs) and deep eutectic solvents (DESs) to make the carbon capture process more sustainable. In the present study, the viscosities of six eutectic-based solvents have been measured within a temperature range of 303.2−330.2 K and have been modeled using a Vogel−Fulcher− Tammann (VFT)-type equation. The results showed that guanidium malate-based eutectic solvents have significantly lower viscosities than most other deep eutectic solvents. Additionally, CO 2 solubilities in three different guanidium-based eutectic solvents have been measured within a temperature range of 313.2−333.2 K and pressures of up to 200 kPa. Henry's law constants of CO 2 in pure solvents were obtained by modeling the solubility in mixed (aqueous) solvents. The values obtained for Henry's law constants of CO 2 in the studied guanidium-based eutectic solvents were found to lie within a range of 1.3−24 MPa. The values of the Gibbs free energy and the dissolution enthalpy and entropy showed that the CO 2 absorption is exothermic, and after CO 2 absorption, the entropy of the systems decreased.

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