Investigation of CO₂ Absorption and Physicochemical Properties of Deep Eutectic Solvents Based on Amine Hydrohalides and Alkanolamines

This study focused on deep eutectic solvents (DESs) comprising ethylamine hydrochloride (EACl), butylamine hydrobromide (BABr), and octylamine hydrobromide (OABr) as hydrogen bond acceptors, paired with alkanolamines (monoethanolamine, 1-aminopropan-2-ol, 2-(methylamino)ethanol, and 3-amino-1-propanol) as hydrogen bond donors. The CO2 capture and phase transitions in these DESs were thoroughly investigated. Structural changes induced by CO2 absorption were examined using NMR and FTIR spectroscopy. Temperature-dependent physicochemical properties, including density and viscosity, were measured and modeled using linear equations and the Vogel–Tammann–Fulcher equation, respectively. The effects of the alkyl chain length of the salt cation and the structure of the alkanolamine on CO2 absorption capacity and physicochemical properties were systematically analyzed. Among the DESs studied, the combination of EACl and monoethanolamine demonstrated a notable CO2 absorption capacity of 0.27 g CO2 per g DES. Quantum chemical calculations were employed to elucidate the interaction mechanisms between EACl and monoethanolamine, as well as their interactions with CO2.