Unveiling the mechanism of CO₂-driven phase change in amine + water + glycol ether ternary mixture

Background: Phase separation solvents have been developed for CO₂ capture with the advantage of low regeneration energy. Understanding the mechanism of phase change driven by CO₂ capture is critical toward design of phase separation solvents. Methods: In this work, the molecular information of σ-profile and simulated ternary liquid–liquid equilibrium (LLE) phase diagram obtained from a predictive modeling based on COSMO-SAC method is used to investigate the phase behavior of phase separation solvents before and after CO₂ absorption. Significant findings: Ternary mixtures of three selected amines [2-aminoethanol (MEA), 2-(ethylamino)ethanol (EAE), 2-(butylamino)ethanol (BAE)] + water + glycol ether, with different strengths of hydrophilicity of amines, exhibit three types of partially miscible behaviors. Upon absorption of CO₂, amine reacts to form hydrophilic reaction products (carbamate + protonated amine), resulting in the change of the molecular interactions and immiscible behaviors. Our study shows that amines, such as EAE, having a balanced interaction with water and glycol ether (exhibiting small immiscible region) are potential candidates for amine + water + glycol ether based phase separation solvent for CO₂ capture.