The separation and capture process of carbon dioxide from power plants is garnering interest as a method to reduce greenhouse gas emissions. In this study, aqueous alkanolamine solutions were studied as absorbents for CO 2 capture. The solubility of CO 2 in aqueous alkanolamine solutions was investigated with a continuous stirred reactor at 313, 333 and 353 K. Also, the heat of absorption (−ΔH abs ) between the absorbent and CO 2 molecules was measured with a differential reaction calorimeter (DRC) at 298 K. The solubility and heat of absorption were determined at slightly higher than atmospheric pressure. The enthalpies of CO 2 absorption in monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), and 2-amino-2-methyl-1-propanol (AMP) were 88.91, 70.44, 44.72, and 63.95, respectively. This investigation showed that the heat of absorption is directly related to the quantity of heat for absorbent regeneration, and is dependent on amine type and CO 2 loading.

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Alkyl amines, which have multiple amino groups, are used as activators to improve the CO2 absorption performances of aqueous methyldiethanolamine (MDEA) solutions. The aqueous MDEA blends consisted of 20% (w/w) of MDEA and 10% (w/w) of activators, which are 3-methylamino propylamine (MAPA), diethylenetriamine (DETA), triethylene tetramine (TETA), and tetraethylenepentamine (TEPA). Aqueous solutions of monoethanolamine (MEA; 30% (w/w)) and MDEA (30% (w/w)) are used as reference absorbents for comparison. The CO2 absorption performances of aqueous MDEA blends were investigated by measurements of absorption capacities, absorption rates, and heats of absorption. The MDEA blends have higher CO2 absorption capacities than MEA and MDEA. MDEA/TEPA shows the highest CO2 loading amount of 0.753 mol-CO2·mol-absorbent–1 at 313 K. In addition, the MDEA blends show high cyclic capacities (0.241–0.330 mol-CO2·mol-absorbent–1), the values of which are about 3 times higher than that of MEA. All MDEA blends show higher absorption fluxes than MDEA. The MDEA/MAPA showed the highest overall mass transfer coefficient of 3.351 × 103 mol·m–2·s–1·kPa–1, 8 times higher than that of MDEA (0.451 × 103 mol·m–2·s–1·kPa–1) and even higher than that of MEA (3.014 × 103 mol·m–2·s–1·kPa–1). The heats of absorption of the MDEA blends (57.21–59.53 kJ·mol-CO2 –1) are about 30% higher than that of MDEA and about 30% lower than that of MEA.

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