Comparison of the CO sub(2) Absorption Characteristics of Aqueous Solutions of Diamines: Absorption Capacity, Specific Heat Capacity, and Heat of Absorption

Aqueous amine solutions have been widely used for the absorption of carbon dioxide (CO sub(2)) from the gas mixtures. An understanding of the physical and chemical properties of aqueous amine solutions is important for the successful design and operation of CO sub(2) absorption processes. Particularly, the absorption capacity, absorption rate, and heat of absorption of CO sub(2) are major factors that affect the CO sub(2) absorption and stripping performance. A comparison study of the aqueous piperazine (PZ), 2-methylpiperazine (2-MPZ), homopiperazine (HomoPZ), and hexamethylenediamine (HMDA) solutions was conducted in this study. Absorption capacities and heats of absorption of these diamine solutions were measured using a semibatch-type reactor and a differential reaction calorimeter (DRC). The species distributions of the absorbents were investigated using a nuclear magnetic resonance spectroscopy (NMR), and the CO sub(2) absorption mechanism was also discussed. Aqueous PZ and PZ derivative solutions (2-MPZ and HomoPZ) displayed excellent characteristics as CO sub(2) absorbents. Aqueous 10 wt % PZ and PZ derivative solutions had higher absorption capacities and lower heats of absorption than that of aqueous 10 wt % monoethanolamine (MEA) at 313 K (- Delta H sub(abs) of the CO sub(2)-saturated PZ, 2-MPZ, HomoPZ, and MEA solutions: 62, 58, 68, and 80 kJ/mol CO sub(2)).