Carbon Dioxide Absorption Heat in Liquid–Liquid and Solid–Liquid Phase-Change Solvents Using Continuous Calorimetry

For three groups of systems—homogeneous, liquid–liquid, and solid–liquid—absorption heats of carbon dioxide capture by amine solutions were determined with continuous calorimetry. In the case of a phase-separation solvent, the heat of phase separation is added to conventional absorption heat, and the loading range of heat of phase separation is important in process design. With the merits of continuous measurement, the phase-change loading points were obtained in liquid–liquid and solid–liquid phase-separation systems as the heat release of carbon dioxide products to achieve a more stable state. The loading points where a leap in absorption heat appears coincide with those where the turbidity in solvents changes, which was confirmed by ocular inspection in both systems. In liquid–liquid systems, the presence of water in 2-(ethylamino)ethanol:diethylene glycol diethyl ether:water contributes to the decrease in absorption heat. Even though the formation of bicarbonate is minor even in solvent with water, the increase in its formation contributes to this decrease in absorption heat because of its lower formation heat as compared to that of carbamate. In solid–liquid systems, a significant increase in absorption heat is attributed to the crystallization energy of carbonate salt emitted on the breakdown of the supersaturation.