Effect of temperature, pressure, and composition on CO 2 solubility in choline chloride-based deep eutectic solvents

Abstract

Carbon dioxide (CO₂) capture is conventionally performed using aqueous monoethanolamine (MEA), but its industrial application is limited by high regeneration energy, solvent degradation, corrosion, and environmental concerns. Deep eutectic solvents (DESs) have emerged as promising alternatives because of their low volatility, simple preparation, and tunable physicochemical properties. This study investigated the physicochemical characteristics and CO₂ absorption performance of choline chloride (ChCl)-polyethylene glycol (PEG-400) DESs with molar ratios of 1:9 and 1:10. The closely spaced PEG-rich compositions of 1:9 and 1:10 were selected to determine whether a small increase in PEG-400 content produces a measurable improvement in CO₂ absorption. The formation of low-melting DES mixtures was supported by the combined results of FTIR spectroscopy, melting-point, and density measurements. CO₂ solubility was measured at 303.15 and 323.15 K over a pressure range of 2.7–23 bar using the constant-volume equilibrium method. CO₂ solubility increased with pressure and decreased with temperature, indicating a predominantly physical absorption process governed by Henry’s law. The highest CO₂ mole fraction (0.2826) was obtained for the ChCl:PEG-400 (1:9) DES at 303.15 K and 23.10 bar. Henry constants ranged from 64.93 to 71.67 bar with less than 3% variation between the two DES formulations. The obtained CO₂ solubility and Henry-constant data provide a thermodynamic data and evaluating the sensitivity of CO₂ solubility to a narrow PEG-rich composition range for CO₂ capture applications.